Computer system having an expansion device for virtualizing a migration source logical unit

ABSTRACT

A migration destination storage creates an expansion device for virtualizing a migration source logical unit. A host computer accesses an external volume by way of an access path of a migration destination logical unit, a migration destination storage, a migration source storage, and an external volume. After destaging all dirty data accumulated in the disk cache of the migration source storage to the external volume, an expansion device for virtualizing the external volume is mapped to the migration destination logical unit.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.11/478,611, filed Jul. 3, 2006, now U.S. Pat. No. 7,461,196, whichrelates to and claims priority from Japanese Patent Application No.2006-136869, filed on May 16, 2006, the entire disclosure of which areincorporated herein by reference.

BACKGROUND

The present invention relates to a computer system having a storagesystem employing storage virtualization technology.

Amidst the rapid advancement of information systems through expansion ofInternet business and electronic management of procedures, the datavolume sent and received by computers is increasing exponentially. Inaddition to this kind of exponential increase in data volume, the datavolume to be stored in storages is also increasing exponentially due tobackup of data in disk devices (Disk-to-Disk Backup) and prolongedstorage of business activity records (transaction information andemails) of companies required in audits. In connection with this,corporate information systems are seeking the reinforcement of storagesin the respective business divisions/respective systems, and thesimplification and streamlining in managing the complex ITinfrastructure. In particular, expectations are increasing fortechnology capable of simplifying the management of storages andoptimizing the total cost by utilizing the optimal storage according tothe value of data.

As a method of reducing management costs of systems having large-scalestorages, there is storage virtualization technology disclosed inJapanese Patent Laid-Open Publication No. 2005-011277. Japanese PatentLaid-Open Publication No. 2005-011277 discloses storage virtualizationtechnology (hereinafter also referred to as “external storage connectingtechnology”) which connects a storage system (hereinafter referred to asa “first storage system”) connected to a host computer to one or moreexternal storage systems (hereinafter referred to as “second storagesystems”), virtualizing a device (hereinafter referred to as an“external device”) having a second storage system as though it is alogical device in the first storage system, and providing this to thehost computer. When the first storage system receives an I/O request tothe logical device from the host computer, it determines whether thedevice of the access destination corresponds to the external device inthe second storage system, or corresponds to a physical device (internaldevice) such as a disk device mounted on the first storage system, andsorts the I/O request to the appropriate access destination according tothe determination result.

As a result of using a storage system employing the external storageconnecting technology described in Japanese Patent Laid-Open PublicationNo. 2005-011277, it is possible to create a system integrating aplurality of storage systems having different attributes such asperformance, reliability, price and so on. For instance, it is possibleto connect a high cost, high function and highly reliable first storagesystem using the external storage connecting technology and a low cost,low function and unreliable second storage system, logically hierarchizethe storage extents, and optimally dispose data according to the updatetime of data and value of data. As a result of using the storage systemhaving hierarchized storage extents, it is possible to store, for a longperiod of time, vast amounts of information such as transactioninformation and emails arising in the daily business activities withappropriate costs according to the value of each type of information forthe purpose of dealing with audits.

Meanwhile, in order to store large capacity data across several tenyears exceeding the life of the storage system, it will be necessary toreplace the equipment configuring the computer system during the storageperiod of data. Japanese Patent Laid-Open Publication No. 2005-011277discloses the copying and migration of data in a logical unit of themigration source storage (hereinafter referred to as a “migration sourcelogical unit”) to a logical unit of the migration destination storage(hereinafter referred to as a “migration destination logical unit”) inorder to replace the first storage system (hereinafter referred to as a“migration source storage”) employing the external storage connectingtechnology with another first storage system (hereinafter referred to asa “migration destination storage”).

SUMMARY

Nevertheless, by performing the copy processing from the migrationsource logical unit to the migration destination logical unit, there isconcern that an adverse effect, such as deterioration in throughput, maybe inflicted on the I/O processing of devices performed by the migrationsource storage. In addition, since it is necessary to copy all data inthe migration source logical unit to the migration destination logicalunit, there is a problem in that much time is required in the devicetakeover from the migration source storage to the migration destinationstorage.

Further, due to the complication of the storage hierarchy, in additionto cases where the migration source logical unit and the external devicecorrespond one-on-one, there may be cases where the two do notcorrespond one-on-one. In particular, even in cases when the migrationsource logical unit and the external device do not correspondone-on-one, it is desirable to enable data migration in units of logicalunits as units of the storage extent recognized by the host computer.

Thus, an object of the present invention is to enable the performance ofdata migration in units of logical units accompanying the change inconfiguration while suppressing performance deterioration of a storagesystem in a computer system employing storage virtualization technology.

Another object of the present invention is to enable the sharing of anexternal volume with a plurality of storage systems in a computer systememploying storage virtualization technology.

In order to achieve the foregoing objects, the computer system of thepresent invention includes a host computer, an external storage systemhaving an external volume, a first storage system having a firstexpansion device configured by virtualizing the external volume, and afirst logical unit configured by virtualizing the first expansion deviceand recognizable from the host computer, and a second storage systemhaving a second expansion device configured by virtualizing the externalvolume, and a second logical unit configured by virtualizing the secondexpansion device and recognizable from the host computer.

Here, for instance, the external storage system controls the exclusiveaccess of either the first or second storage system regarding therespective storage extents configuring the external volume.

The host computer, for example, executes path switching for connectingto a storage system having the access right regarding the respectivestorage extents configuring the external volume.

The external volume may include a shared extent to be accessed from boththe first and second storage systems.

The computer system according to another aspect of the present inventionincludes a host computer, an external storage system having an externalvolume, a first storage system having a first expansion deviceconfigured by virtualizing the external volume, and a first logical unitconfigured by virtualizing the first expansion device via anintermediate storage hierarchy so as to become recognizable from thehost computer, and a second storage system connectable to the hostcomputer and the external storage system. Upon receiving a command tomigrate the first logical unit from the first storage system to thesecond storage system, the second storage system creates a secondexpansion device for virtualizing the external volume in the secondstorage system, creates a third expansion device for virtualizing thefirst logical unit in the second storage system, defines a path forconnecting the first logical unit and the third expansion device,creates a second logical unit configured by virtualizing the thirdexpansion device via an intermediate storage hierarchy in the secondstorage system so as to become recognizable from the host computer, andsets a path for connecting the second logical unit and the host computeras an alternate path of a path for connecting the first logical unit andthe host computer. The host computer, by way of the alternate path,accesses the external volume from the second logical unit via anintermediate storage hierarchy in the second storage system, a pathconnecting the first and the second storage system, the first logicalunit, and an intermediate storage hierarchy in the first storage system.When all data written from the host computer to the second logical unitis written in the external volume, the second storage system releasesthe relation between the third expansion device and the second logicalunit, and associates the second expansion device with the second logicalunit.

The first storage system further has a disk cache for temporarilystoring data to be read from and written into the first logical volume.Upon receiving a command to migrate the first logical unit from thefirst storage system to the second storage system, the first storagesystem sets the operation mode of the first storage system to a cachethrough mode.

The intermediate storage hierarchy in the first storage system includesa virtual device for virtualizing the first expansion device, and thefirst logical unit is configured by virtualizing a part of the virtualdevice.

The first storage system is inhibited from accessing the storage extentcorresponding to a part of the virtual device among the storage extentsconfiguring the external volume.

The intermediate storage hierarchy in the first storage system includesa logical device for virtualizing the first expansion device, and thefirst logical unit is configured by consolidating and virtualizing aplurality of logical devices.

The intermediate storage hierarchy in the first storage system includesa virtual device for virtualizing the expansion device by applying aRAID configuration to the storage extent of the first expansion device,and the first logical unit is configured by virtualizing a part of thevirtual device.

The external volume includes a first storage extent for storing userdata to be read and written by the host computer, and a second storageextent for storing management information of the first logical unit. Theintermediate storage hierarchy in the first storage system includes alogical device for virtualizing the first expansion device. The logicaldevice includes a first storage extent for virtualizing the firststorage extent of the external volume, and a second storage extent forvirtualizing the second storage extent of the external volume. The firstlogical unit is configured by virtualizing the first storage extent ofthe logical device.

The second storage system sets the management information stored in thesecond storage extent of the external volume as attribute information ofthe second logical unit.

The computer system of the present invention may further have a functionof migrating a plurality of first logical units from the first storagesystem to the second storage system.

The computer system of the present invention may further have a functionof migrating a part of the first logical unit from the first storagesystem to the second storage system.

In the computer system of the present invention, the first logical unitstores a plurality of file systems, and a part of the logical unit isone or more file systems among the plurality of file systems.

In the computer system of the present invention, the external storagesystem exclusively accepts the access from the second storage systemregarding a storage extent corresponding to a part of the first logicalunit among the storage extents configuring the external volume, andexclusively accepts the access from the first storage system regarding astorage extent corresponding to portions excluding a part of the firstlogical unit among the storage extents configuring the external volume.

In the computer system of the present invention, the host computerexecutes path switching for connecting to a storage system having anaccess right regarding the respective storage extents configuring theexternal volume.

In the computer system of the present invention, the function forencrypting data to be written by the second storage system in the thirdexpansion device is set up as OFF, and the function for encrypting datato be written by the first storage system in the first expansion deviceis set up as ON.

The computer system of the present invention includes a host computer,an external storage system having an external volume, a plurality offirst storage systems having a first expansion device configured byvirtualizing the external volume, and a first logical unit configured byvirtualizing the first expansion device via an intermediate storagehierarchy so as to become recognizable from the host computer, a secondstorage system connectable to the host computer and the external storagesystem, and a management server to be connected to the first and thesecond storage systems. The management server sets a storage systemsubject to failure or performance deterioration among the plurality offirst storage systems as a migration source storage system, sets thefirst logical unit of the migration source storage system as a migrationsource logical unit, and sets the second storage system as a migrationdestination storage system. The migration destination storage systemcreates a second expansion device for virtualizing the external volumein the migration destination storage system, creates a third expansiondevice for virtualizing the migration source logical unit in themigration destination storage system, defines a path for connecting themigration source logical unit and the third expansion device, creates amigration destination logical unit configured by virtualizing the thirdexpansion device via an intermediate storage hierarchy in the migrationdestination storage system so as to become recognizable from the hostcomputer, and sets a path for connecting the migration destinationlogical unit and the host computer as an alternate path of a path forconnecting the migration source logical unit and the host computer. Thehost computer, by way of the alternate path, accesses the externalvolume from the migration destination logical unit via an intermediatestorage hierarchy in the migration destination storage system, a pathconnecting the migration destination storage system and the migrationsource storage system, the migration source logical unit, and anintermediate storage hierarchy in the migration source storage system.When all data written from the host computer to the migrationdestination logical unit is written in the external volume, the secondstorage system releases the relation between the third expansion deviceand the migration destination logical unit, and associates the secondexpansion device with the migration destination logical unit.

The computer system of the present invention includes a host computer,an external storage system having an external volume, a first storagesystem having a first expansion device configured by virtualizing theexternal volume, and a first logical unit configured by virtualizing thefirst expansion device via an intermediate storage hierarchy so as tobecome recognizable from the host computer, and a second storage systemhaving a second expansion device configured by virtualizing the externalvolume, and a second logical unit configured by virtualizing the secondexpansion device via an intermediate storage hierarchy so as to becomerecognizable from the host computer. The first expansion device isconfigured by virtualizing the second logical unit. A path forconnecting the second logical unit and the host computer is set as analternate path of a path for connecting the first logical unit and thehost computer. The host computer access the external volume from thefirst logical unit via an intermediate storage hierarchy in the firststorage system, a path connecting the first and the second storagesystems, the second logical unit, and an intermediate storage hierarchyin the second storage system. When all data written from the hostcomputer to the first logical unit is written in the external volume,the host computer accesses the second logical unit by way of thealternate path.

According to the present invention, it is possible to perform datamigration in units of logical units accompanying the change inconfiguration while suppressing performance deterioration of a storagesystem in a computer system employing storage virtualization technology.

In addition, according to the present invention, it is to possible toshare an external volume with a plurality of storage systems in acomputer system employing storage virtualization technology.

DESCRIPTION OF DRAWINGS

FIG. 1 is a principle diagram of logical unit migration processingaccording to an embodiment of the present invention;

FIG. 2 is a network configuration relating to an embodiment of thepresent invention;

FIG. 3 is an explanatory diagram of a storage hierarchy configured in astorage system;

FIG. 4 is an explanatory diagram showing a mapping relation of the CVSconfiguration;

FIG. 5 is an explanatory diagram showing a mapping relation of the LUSEconfiguration;

FIG. 6 is an explanatory diagram showing a mapping relation of theexternal volume RAID configuration;

FIG. 7 is an explanatory diagram of the VMA volume;

FIG. 8 is an explanatory diagram of the mainframe volume;

FIG. 9 is an explanatory diagram showing a mapping relation of the VDEVconsolidation;

FIG. 10 is an explanatory diagrams showing a mapping relation of theVDEV discrete;

FIG. 11 is an explanatory diagram showing a mapping relation of the VDEVdiscrete;

FIG. 12 is an explanatory diagram showing a mapping relation of the VDEVdiscrete;

FIG. 13 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 14 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 15 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 16 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 17 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 18 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 19 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 20 is an explanatory diagram showing the DEVGr-EDEV/PDEV mappingrelation;

FIG. 21 is an explanatory diagram showing the AOU configuration;

FIG. 22 is an explanatory diagram showing a storage hierarchy of thesnapshot function;

FIG. 23 is an explanatory diagram relating to a host group;

FIG. 24 is an explanatory diagram relating to an alternate path;

FIG. 25 is an explanatory diagram relating to an alternate path;

FIG. 26 is an explanatory diagram of host group management information;

FIG. 27 is an explanatory diagram of LU path management information;

FIG. 28 is an explanatory diagram of logical device managementinformation;

FIG. 29 is an explanatory diagram of virtual device managementinformation;

FIG. 30 is an explanatory diagram of device group managementinformation;

FIG. 31 is an explanatory diagram of VDEV-DEVGr mapping information;

FIG. 32 is an explanatory diagram of physical device managementinformation;

FIG. 33 is an explanatory diagram of expansion device managementinformation;

FIG. 34 is a software configuration of a computer system;

FIG. 35 is an explanatory diagram showing the outline of processing formigrating a logical unit having a CVS configuration;

FIG. 36 is an explanatory diagram showing the outline of processing formigrating a logical unit having a LUSE configuration;

FIG. 37 is an explanatory diagram showing the outline of processing formigrating a logical unit having an external volume RAID configuration;

FIG. 38 is an explanatory diagram showing the outline of processing formigrating a logical unit having a VMA volume configuration;

FIG. 39 is an explanatory diagram showing the outline of processing formigrating a logical unit having a VMA volume configuration;

FIG. 40 is an explanatory diagram showing the outline of processing formigrating a logical unit having a mainframe volume configuration;

FIG. 41 is an explanatory diagram showing the outline of processing formigrating a plurality of logical units;

FIG. 42 is an explanatory diagram showing the logical unit migrationcommand processing routine;

FIG. 43 is an explanatory diagram showing the logical unit migrationprocessing subroutine;

FIG. 44 is an explanatory diagram showing the migration target selectionprocessing subroutine;

FIG. 45 is an explanatory diagram showing the migration preparationprocessing subroutine;

FIG. 46 is an explanatory diagram showing the migration processingsubroutine;

FIG. 47 is an explanatory diagram showing the storage I/O processingroutine;

FIG. 48 is an explanatory diagram showing the host I/O processingroutine;

FIG. 49 is an explanatory diagram showing the storage load monitoringprocessing routine;

FIG. 50 is an explanatory diagram showing another method of performinglogical unit migration processing;

FIG. 51 is an explanatory diagram showing another method of performinglogical unit migration processing;

FIG. 52 is an explanatory diagram showing another method of performinglogical unit migration processing;

FIG. 53 is an explanatory diagram showing another method of performinglogical unit migration processing;

FIG. 54 is an explanatory diagram showing another method of performinglogical unit migration processing;

FIG. 55 is an explanatory diagram showing the outline of processing formigrating a part of the logical unit;

FIG. 56 is an explanatory diagram showing the outline of processing formigrating a part of the logical unit;

FIG. 57 is a system configuration of the high-availability computersystem;

FIG. 58 is a system configuration of the high-availability computersystem; and

FIG. 59 is a system configuration of the high-availability computersystem.

DETAILED DESCRIPTION

Embodiments of the present invention are now explained with reference tothe attached drawings. Foremost, the principle of logical unit migrationprocessing of the present embodiment is explained with reference toFIG. 1. The computer system 500 pertaining to this embodiment includes ahost computer 100, a plurality of storage systems 130 a, 130 b, and anexternal storage system 150.

The storage system 130 a has one or more logical units (LU) 201 a. A LUN(Logical Unit Number) is assigned to the logical unit 201 a. The logicalunit 201 a is provided to the host computer 100 as a logical storageextent. The host computer 100 is able to write data in the logical unit201 a and read data from the logical unit 201 a. A plurality ofintermediate storage hierarchies (LDEV/VDEV/EDEV) are provided to thelower layer of the logical unit 201 a. The intermediate storagehierarchy is a logical storage resource for associating the logical unit201 a and the external volume 301. Access from the host computer 100 isconveyed from the logical unit 201 a to the external volume 301 via theintermediate storage hierarchy.

For instance, a logical device (LDEV) 202 a, a virtual device (VDEV) 203a, and an expansion device (EDEV) 206 a may be included in theintermediate storage hierarchy in the storage system 130 a. Each ofthese devices is not necessarily required, and certain devices may beomitted. Further, in addition to each of these devices, other devices(for instance, a device group (DEVGr) or the like described later)(refer to FIG. 3) may also be included.

Incidentally, as shown in FIG. 3, when the storage system 130 has aphysical device (PDEV) 205, the physical device 205 and the expansiondevice 206 both belong to the same intermediate storage hierarchy.

For convenience of explanation, there are times when the storagehierarchy to which the logical unit belongs is referred to as a “LDEVhierarchy”. Similarly, there are times when the storage hierarchy towhich the logical device belongs is referred to as a “LDEV hierarchy”,when the storage hierarchy to which the virtual device belongs isreferred to as a “VDEV hierarchy”, and when the storage hierarchy towhich the physical device and/or expansion device belongs is referred toas a “PDEV/EDEV hierarchy”.

The storage system 130 a includes one or more ports 131 a for connectingto the host computer 100 via a path 401, a logical unit 201 a allocatedto a port 131 a, a logical device 202 a mapped to a logical unit 201 a,a virtual device 203 a mapped to a logical device 202 a, and anexpansion device 206 a mapped to a virtual device 203 a. Here, “mapping”refers to the association of an address space of a certain device withan address space of another device. In this specification, to map acertain device to another device is synonymous with associating (orallocating) a certain device with (to) another device.

The storage system 130 a is connected to the external storage system 150via a path 402. The external storage system 150 has an external volume301 defined on a physical device having a real storage extent such as adisk drive.

Here, the expansion device 206 a is a virtualization of the externalvolume 301 as the storage resource existing outside the storage system130 a. In other words, the expansion device 206 a is a storage hierarchyconfigured by virtualizing the external storage resource.

The virtual device 203 a is a storage hierarchy for connecting anupper-level storage hierarchy (for instance LU/LDEV) and a lower-levelstorage hierarchy (for instance DEVGr/EDEV). When the lower-levelstorage hierarchy is a physical device, the virtual device 203 a, forexample, is a storage hierarchy configured by configuring the storageextents provided respectively from a plurality of physical devices in aRAID configuration. Meanwhile, when the lower-level storage hierarchy isan expansion device 206 a, the virtual device 203 a, for example, is astorage extent configured by assembling all or a part of the respectivestorage extents of the plurality of expansion devices 206 a, or astorage extent configured by extracting a part of the storage extent ofthe expansion device 206 a.

The logical device 202 a, for example, is a storage extent configured byassembling all or a part of the respective storage extents of theplurality of virtual devices 203 a, or a storage extent configured byextracting a part of the storage extent of the virtual device 203 a.When the host computer 100 is an open system, the host computer 100recognizes the logical device 202 a as one physical device, and accessesthe desired logical device 202 a by designating the LUN or logical blockaddress. When the host computer 100 is a mainframe system, the hostcomputer 100 directly recognizes the logical device 202 a.

The logical unit 201 a is a virtualization of the external volume 301,and is also a logical storage extent recognized by the host computer100. For example, when the host computer 100 is a UNIX (registeredtrademark) system, the logical unit 201 a is associated with a devicefile. Meanwhile, when the host computer 100 is a Windows (registeredtrademark) system, the logical unit 201 a is associated with a driveletter (drive name). A unique LUN (Logical Unit Number) is assigned tothe logical unit 201 a.

For the convenience of explaining the logical unit migration processing,the relation between the logical unit 201 a and the logical device 202 awill be one-on-one, the relation between the logical device 202 a andthe virtual device 203 a will be one-on-one, the relation between thevirtual device 203 a and the expansion device 206 a will be one-on-one,and the relation between the expansion device 206 a and the externalvolume 301 will be one-on-one. Under the foregoing relation, the storagecapacity of the logical unit 201 a recognized by the host computer 100is equivalent to the storage capacity of the external volume 301.

Meanwhile, the storage system 130 b has a plurality of storagehierarchies that are hierarchized as with the storage system 130 a. Thestorage system 130 b includes one or more ports 131 b for connecting tothe host computer 100 via a path 403, a logical unit 201 b allocated tothe port 131 b, a logical device 202 b mapped to a logical unit 201 b, avirtual device 203 b mapped to a logical device 202 b, and expansiondevices 206 c, 206 b mapped to a virtual device 203 b.

For the convenience of explaining the logical unit migration processing,the relation between the logical unit 201 b and the logical device 202 bwill be one-on-one, the relation between the logical device 202 b andthe virtual device 203 b will be one-on-one, the relation between thevirtual device 203 b and the expansion device 206 c will be one-on-one,the relation between the virtual device 203 b and the expansion device206 b will be one-on-one, the relation between the expansion device 206c and the logical unit 201 a will be one-on-one, and the relationbetween the expansion device 206 b and the external volume 301 will beone-on-one. Further, the expansion device 206 c and the expansion device206 b have the same storage capacity, and either the expansion device206 c or the expansion device 206 b is selectively mapped to the virtualdevice 203 b.

The outline of processing for migrating data of the logical unit 201 a(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines a path 405 for externallyconnecting the external volume 301 and the storage system 130 b, andcreates an expansion device 206 b for virtualizing the external volume301 in the storage system 130 b.

(2) The storage system 130 b creates a virtual device 203 b having astorage capacity that is the same as the storage capacity of theexternal volume 301 in the storage system 130 b.

(3) The storage system 130 b defines a path 404 for externallyconnecting the logical unit 201 a and the storage system 130 b, andcreates an expansion device 206 c for virtualizing the logical unit 201a in the storage system 130 b.

(4) The storage system 130 b maps the expansion device 206 c to thevirtual device 203 b.

(5) The storage system 130 b creates a logical device 202 b having alogical configuration that is the same as the logical configuration ofthe logical device 202 a in the storage system 130 b. The virtual device203 b is mapped to the logical device 202 b.

(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Thelogical device 202 b is mapped to the logical unit 201 b.(7) The host computer 100 switches the path 401 to the path 403 as apath for accessing the external volume 301. Here, access from the hostcomputer 100 to the logical unit 201 a is inhibited such as by deletingthe path 401. Incidentally, path switching from the path 401 to the path403 may also be conducted by the storage systems 130 a, 130 b, or themanagement server 110. Further, it is not necessarily the case that thepath 401 needs to be deleted, and, for instance, the path 401 may be setas an alternate path (for instance, a path to be used during systemfailure) of the path 403, and the path 401 may be left as is with thepath 401 in an invalid state.

As a result of the foregoing processing, not only is the logical unit201 b a virtualization of the logical unit 201 a, it is also avirtualization of the external volume 301. Thus, the data I/O path fromthe host computer 100 to the logical unit 201 a during the logical unitmigration processing will be path 403→storage hierarchy(LU/LDEV/VDEV/EDEV) in the storage system 130 b →path 404→storagehierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130 a →path402→external volume 301.

Incidentally, when the storage systems 130 a, 130 b involved in thelogical unit migration processing are equipped with an encryptionfunction, there are cases when it is not possible to decrypt datawritten in the external volume 301 if the encryption function of the twostorage systems 130 a, 130 b is set to be ON. In the foregoing case, theencryption function of the storage system 130 b is set to be OFF, andthe encryption function of the storage system 130 a is set to be ON. Inother words, data written in the expansion device 206 c is not encrypteddue to the storage system 130 b, and data written in the expansiondevice 206 a is not encrypted due to the storage system 130 a. As aresult of setting the encryption function as described above, since itis possible to limit the number of times data written in the externalvolume 301 is encrypted to once, it is possible to decrypt data writtenin the external volume 301.

(8) The storage system 130 a sets the operation mode of the storagesystem 130 a for destaging to the external volume 301 all dirty dataaccumulated in the disk cache of the storage system 130 a to a cachethrough mode (write through mode). Dirty data refers to unreflected datathat has not been destaged from the disk cache to the external volume301. A cache through mode refers to the operation of receiving a datawrite request from the host computer 100 and storing data in the diskcache, additionally writing such data in a device (internal device orexternal device), and thereafter reporting the completion of updatingdata to the host computer 100. Incidentally, the storage system 130 amay autonomously set the operation mode to a cache through mode, or setthe operation mode to a cache through mode based on an external command(for instance, from the storage system 130 b, the host computer 100, ora management server 110 described later).(9) After destaging all dirty data accumulated in the disk cache of thestorage system 130 a to the external volume 301, the storage system 130b releases the mapping relation between the expansion device 206 c andthe virtual device 203 b, and maps the expansion device 206 b to thevirtual device 203 b. In addition, the storage system 130 b deletes thepath 404.

According to the foregoing method, it is possible to migrate the logicalunit 201 a while continuing the data I/O processing from the hostcomputer 100 to the logical unit 201 a. Thereby, since the role ofperforming I/O processing to the external volume according to the loadfluctuation among the plurality of storage systems 130 resulting fromthe I/O request from the host computer 100 can be switched between theplurality of storage systems 130 a, 130 b, it is possible to realize theload balancing of the computer system 500. In addition, by setting theoperation mode of the migration source storage among the storage systems130 a, 130 b to a cache through mode and setting the operation mode ofthe migration destination storage to a write after mode, it is possibleto perform asynchronous write processing using the disk cache, andsuppress the performance deterioration of the storage system 130 acaused by the logical unit migration processing.

Incidentally, although it is possible to migrate the logical unit 201 aeven if the operation mode of the migration target storage system 130 bto a cache through mode, the migration processing of the logical unit201 a will not be complete unless all dirty data accumulated in themigration source storage system 130 a is destaged to the external volume301. Thus, in order to shorten the migration processing time of thelogical unit 201 a, it is preferable to set the operation mode of themigration source storage system 130 a to a cache through mode.

Further, with the system configuration shown in FIG. 1, although therespective storage systems 130 a, 130 b have an expansion device 206configured by virtualizing the external volume 301, they do not have aninternal device (physical device). The logical unit migration processingpertaining to the present invention is not limited to the application ina system configuration as shown in FIG. 1, and, for instance, may alsobe applied to processing for migrating a logical unit provided by aphysical device such as a disk device built in the storage systems 130a, 130 b that do not have an external volume virtualization function.

In the foregoing explanation of the logical unit migration processing,although a case was illustrated where the mutual mapping relationbetween the respective intermediate storage hierarchies is one-on-onefor the convenience of explanation, the mutual mapping relation betweenthe respective intermediate storage hierarchies is not necessarilylimited to be one-on-one. As the mutual mapping relation between therespective intermediate storage hierarchies, for example, variationssuch as CVS (Custom Volume Size), LUSE (LU Size Expansion), externalvolume RAID, VMA (Volume Management Area) volume, mainframe volume, VDEVconsolidation, VDEV discrete, AOU (Allocation on Use), snapshot and thelike may be considered. Details will be explained in the embodimentsdescribed later (refer to FIG. 4 to FIG. 22).

EMBODIMENTS

FIG. 2 shows a network configuration of the computer system 500pertaining to the present embodiment. The computer system 500 includes aplurality of host computers 100 a, 100 b, one or more management servers110, one or more fibre channel switches 120, a plurality of storagesystems 130 a, 130 b, a plurality of management terminals 140 a, 140 b,and a plurality of external storage systems 150 a, 150 b. In thefollowing explanation, when the host computers 100 a, 100 b are notdifferentiated, they are collectively referred to as a host computer100. When the storage systems 130 a, 130 b are not differentiated, theyare collectively referred to as a storage system 130. When themanagement terminals 140 a, 140 b are not differentiated, they arecollectively referred to as a management terminal 140. When the externalstorage systems 150 a, 150 b are not differentiated, they arecollectively referred to as a storage system 150.

The host computer 100, the storage system 130, and the external storagesystem 150 are respectively connected to a port 121 of a fibre channelswitch 120 via ports 107, 131, 151. Further, the host computer 100, thestorage system 130, the external storage system 150, and the fibrechannel switch 120 are respectively connected from the interfacecontrollers 106, 138, 157, 123 to the management server 110 via an IPnetwork 175. The management server 110 manages these network nodes (hostcomputer 100, storage system 130, external storage system 150, and fibrechannel switch 120).

Incidentally, although the storage system 130 has a networkconfiguration connected to the management server 110 via the managementterminal 140 in this embodiment, the storage system 130 may be of anetwork configuration to be directly connected to the IP network 175.

The host computer 100 includes a CPU 101, a memory 102, a storageapparatus 103, an input device 104, a display 105, an interfacecontroller 106, and a port 107. The storage apparatus 103, for instance,is a disk device, a magneto optical disk device or the like. The hostcomputer 100 executes information processing by reading software such asan operating system or an application program stored in the storageapparatus 103 into the memory 102, and making the CPU 101 read andexecute such software. The input device 104 is a keyboard, a mouse orthe like. The host computer 100 accepts input from a host administratoror the like via the I/O device 104, and displays the informationprocessing results and the like on the display 105. The interfacecontroller 106 is a LAN adapter or the like for connecting to the IPnetwork 175. The port 107 is a host bus adapter or the like forconnecting to the storage system 130.

The management server 110 includes a CPU 111, a memory 112, a storageapparatus 113, an input device 114, a display 115, and an interfacecontroller 116. The storage apparatus 113, for instance, is a diskdevice, a magneto optical disk device or the like. The management server110 reads storage management software stored in the storage apparatus113 into the memory 112, and maintains and manages the overall computersystem 500 by making the CPU 111 read and execute such storagemanagement software. When the CPU 111 executes the storage managementsoftware, the management server 110 collects, from the interfacecontroller 116 via the IP network 175, configuration information,resource utilization ratio, performance monitoring information, failurelog and so on from the respective network nodes in the computer system500. The management server 110 thereafter outputs the collectedinformation to an output device such as the display 115 so as to presentsuch information to the storage administrator. The management server 110also accepts commands relating to maintenance and management from thestorage administrator via the input device 114 such as a keyboard or amouse, and sends such commands to the network node.

The storage system 130 has one or more ports 131 for connection to thestorage network, one or more control processors 132 for controlling thedata I/O processing to the disk device 137, one or more memories 133that function as a work area of the respective control processors 132,one or more disk caches 134 for temporarily storing data to be input andoutput to and from the disk device 137, one or more control memories 135for storing configuration information and the like of the storage system130, one or more ports 136 that function as an interface for connectingto the disk device 137, and a disk device 137 for storing data.

The control processor 132 specifies the logical unit of the accessdestination based on information (port ID and LUN) contained in the I/Orequest received from the host computer 100 via the port 131. If thelogical unit of the access destination corresponds with the disk device137 (internal device), the control processor 132 controls the input andoutput of data to and from the disk device 137. If the logical unit ofthe access destination corresponds with the external storage system 150(external device), the control processor 132 controls the input andoutput of data to and from the external storage system 150.

Incidentally, as the port 131, although a port corresponding to a fibrechannel interface having SCSI (Small Computer System Interface) as theupper-level protocol is assumed in this embodiment, the port 131 mayalso be a port corresponding to an IP network interface having SCSI asthe upper-level protocol.

The storage system 130 has the following storage hierarchy. A disk arrayis configured from a plurality of disk devices 137, and this disk arrayis managed as a physical device by the control processor 132. Further,the control processor 132 allocates a logical device to the physicaldevice mounted in the storage system 130 (that is, the control processor132 associates the physical device with the logical device). The logicaldevice is managed in the storage system 130, and its LDEV number ismanaged independently in each storage system 130.

The logical device is associated with the LUN allocated to each port131, and is provided to the host computer 100 as a device in the storagesystem 130. In other words, what the host computer 100 recognizes is thelogical device in the storage system 130, and the host computer 100 usesthe LUN for identifying the logical device allocated to the port 131 inorder to access the data stored in the storage system 130.

In this embodiment, the control processor 132 manages the logical devicein the external storage 150 as an external device, and virtualizes it asa device (internal device) in the storage system 130. In other words,the external device managed by the storage system 130 is a virtualdevice. The external device incorporated into the storage system 130with the external storage connecting technology is managed as a logicaldevice in the storage system 130 as with the physical device in thestorage system 130.

In order to realize the foregoing storage hierarchy, the controlprocessor 132 manages the relation of the logical device, physicaldevice, and disk device 13 in the storage system 130, and the logicaldevice and disk device 156 in the external storage system 150. Thecontrol processor 132 converts the I/O request from the host computer100 into an access request to the disk device 137 in the storage system130, or into an access request to the disk device 156 in the externalstorage system 150.

As described above, the storage system 130 of this embodiment definesone or more physical devices by consolidating the storage extents of aplurality of disk devices 137 (that is, it consolidates the storageextents of a plurality of disk devices 137 and associates it with one ormore physical devices), allocates one logical device to one physicaldevice, and provides the storage extent to the host computer 100. Eachdisk device 137 may also be associated with one physical device.

The control processor 132 controls the data I/O processing to thedevice, as well as controls the data replication and data rearrangementbetween the volumes. The control processor 132 is connected to themanagement terminal 140 via the interface controller 138, and may alsoreceive the configuration change command input by the storageadministrator into the management terminal 140, and change theconfiguration of the storage system 130.

The disk cache 134 temporarily stores the data to be input and outputbetween the host computer 100 and the disk device 137. The processing ofstoring data received by the storage system 130 from the host computer100 in the disk cache 134, returning a write completion report to thehost computer 100, and thereafter destaging the data to the disk device137 is referred to as write after processing.

When the storage system 130 is configured to perform write afterprocessing, in order to prevent the data stored in the disk cache 134from becoming lost before being written into the disk device 137, it ispreferable to improve the fault tolerance by backing up the power of thedisk cache 134, or duplexing the disk cache 134.

The control memory 135 stores configuration information of the storagesystem 130 (for instance, mapping information for managing the relationbetween devices, setting information of the cache through mode or thelike). Since the control processor 132 will not be able to access thedisk device 137 if the configuration information stored in the controlmemory 135 is lost, it is preferable to improve the fault tolerance bybacking up the power of the control memory 135, or duplexing the controlmemory 135.

The management terminal 140 includes an interface controller 141, a CPU142, a memory 143, a storage apparatus 144, an input device 145, adisplay 146, and an interface controller 147. The interface controller141 is a communication interface for connecting to the storage system130. The storage apparatus 144, for instance, is a disk device, amagneto optical disk device or the like. The input device 145 is akeyboard, a mouse or the like. The display 146 provides a user interfaceenvironment for storage management, and, for instance, displays theconfiguration information and management information of the storagesystem 130. The CPU 142 refers to the configuration information, changesthe configuration, and commands the operation of specific functions byreading and executing the storage management program stored in thestorage apparatus 144 into the memory 143.

In this embodiment, a network configuration may be adopted where thestorage system 130 is directly connected to the management server 110without going through the management terminal 140, and manages thestorage system 130 with management software that operates on themanagement server 110.

The external storage system 150 includes one or more ports 151 forconnecting to the port 131 of the storage 130 via the fibre channelswitch 120, one or more control processors 152 for controlling the dataI/O processing to the disk device 156, one or more memories 153 thatfunction as a work area of the respective control processors 152, one ormore disk caches 154 for temporarily storing data to be input and outputto and from the disk device 156, one or more ports 155 that function asan interface for connecting the control processor 152 to the disk device156, one or more disk drives 156 for storing data, and an interfacecontroller 157 that functions as an interface for connecting to the IPnetwork.

Since a network configuration where the port 131 equipped in the storagesystem 130 and the port 151 equipped in the external storage system 150are connected via the fibre channel switch 120 is adopted in thisembodiment, it is desirable to set zoning to the fibre channel switch120 in order to prevent the direct access from the host computer 100 tothe external storage system 150. It is not necessarily required toestablish the fibre channel switch 120 on the storage network, and, forinstance, a network configuration where the port 131 equipped in thestorage system and the port 151 equipped in the external storage system150 are directly connected may also be adopted.

FIG. 3 shows a storage hierarchy configured in the storage system 130pertaining to this embodiment. Logical resources and physical resourcesthat are the same as those shown in FIG. 1 and FIG. 2 are given the samereference numeral, and the detailed explanation thereof is omitted.

The host computer 100 includes a link manager 108 and a RAID manager109. The link manager 108 is a software program for switching the accesspath to the storage system 130. The RAID manager 109 is storagemanagement software for managing the storage resource of the storagesystem 130, and gives various commands to the storage system 130 (forinstance, a logical unit migration command).

A certain port 131 equipped in the storage system 130 is connected tothe host computer 100 via the storage network 510, and another port 131is connected to the external storage system 150 via the storage network510. The storage network 510 is a network such as an FC-SAN (FibreChannel Storage Area Network) including one or more fibre channelswitches 120.

The storage system 130 has a storage hierarchy configured from a logicalunit 201, a logical device 202, a virtual device 203, a device group204, a physical device 205, and an expansion device 206. The devicegroup 204, for instance, is a storage extent configured by consolidatingall or a part of the respective storage extents of a plurality ofphysical devices 205 and/or the expansion device 206, or a storageextent configured by extracting a part of the storage extent of thephysical device 205 and/or the expansion device 206.

Incidentally, although the physical device 205 and the expansion device206 differ in that the former is a virtualization of the storage extent(internal device) of the disk device 137 of the storage system 130, andthe latter is a virtualization of the storage extent (external device)of the disk device 156 of the external storage system 150, the both arecommon in that they are virtualizations of real devices, and thereforebelong to the same hierarchy (lowest layer).

The storage system 130 includes a CMD (Command Device) 207 to beallocated to the port 131. The CMD 207 is a logical unit used fortransferring commands and statuses between the host computer 100 and thestorage system 130. Commands sent from the host computer 100 to thestorage system 130 are written in the CMD 207. The storage system 130executes processing corresponding to the commands written in the CMD207, and writes the execution result thereof as a status in the CMD 207.The host computer 100 reads and confirms the status written in the CMD207, and writes the command to be subsequently executed in the CMD 207.Like this, the host computer 100 is able to give various commands to thestorage system 130.

As the contents of commands to be given by the host computer 100 to thestorage system 130, for instance, there is a device migration command(logical unit migration command) in units of logical units or a devicemigration command (logical device migration command) in units of logicaldevices. Outline of the logical unit migration processing is asdescribed above. If the logical unit 201 of the migration source is of aLUSE configuration, the host computer 100 is able to give a logicaldevice migration command to the storage system 130. Since a plurality oflogical devices 202 are mapped to one logical unit 201 in a logical unit201 having a LUSE configuration (refer to FIG. 5), by designating onelogical device 202 (for instance, a logical device 202 allocated to thetop address of the logical unit 201) among the plurality of logicaldevices 202, it is possible to designate all other logical devices 202mapped to the logical unit 201 as the migration target.

Incidentally, when prescribed conditions (for instance, when a failureoccurs in the storage system 130 or when the performance of the storagesystem 130 deteriorates) are satisfied, the storage system 130 mayautonomously (without waiting for a command from the host computer 100)execute the logical unit migration processing. Outline of processing formigrating the logical unit when a failure occurs in the storage system130 or when the performance of the storage system 130 deteriorates willbe described later.

Further, the management server 110 may also give a logical unitmigration command to the storage system 130 via the IP network 175 andthe management terminal 140. In other words, a logical unit migrationcommand may be given from the host computer 100 to the storage system130 via an inbound network (via the storage network), or a logical unitmigration command may be given from the management server 110 to thestorage system 130 via an outbound network (via the IP network).

Variations in the mutual mapping relation between the respective storagehierarchies are now explained with reference to FIG. 4 to FIG. 22.

(1) CVS

As shown in FIG. 4, the mapping relation of partitioning one virtualdevice 203 into a plurality of VDEV extents 203-1, 203-2, 203-3, andallocating one logical device 202 to the respective VDEV extents 203-1,203-2, 203-3 is referred to as CVS. Sizes of the respective VDEV extents203-1, 203-2, 203-3 do not necessarily have to be the same.

(2) LUSE

As shown in FIG. 5, the mapping relation of gathering the storageextents of a plurality of logical devices 202 and allocating them to onelogical unit 201 is referred to as LUSE.

(3) External Volume RAID

As shown in FIG. 6, the mapping relation of allocating an expansiondevice 206 of a RAID configuration to a device group 204 is referred toas an external volume RAID. For example, one expansion device 206 amongthe plurality of expansion devices 206 of a RAID 1 configurationcorresponds to a data disk, and another expansion device 206 correspondsto a mirror disk.

(4) VMA Volume

FIG. 7 shows a VMA volume. A VMA volume is a logical device 202 used inan open system. The logical device 202 has a user extent 202-1 forstoring user data, and a management extent 202-2 for storing managementinformation. Management information, for instance, includes the accessattribute of the VMA volume. Access attribute includes information suchas readable/writable, read only, non-readable/non-writable, readcapacity zero, inquiry inhibit, secondary volume disable (S-VOL disable)and so on. The user extent 202-1 can be recognized by the host computer100 and is allocated to the logical unit 201, whereas the managementextent 202-2 cannot be recognized by the host computer 100, and is notallocated to the logical unit 201.

(5) Mainframe Volume

FIG. 8 shows a mainframe volume. The mainframe volume is a logicaldevice 202 to be used in a mainframe system. The logical device 202 hasa user extent 202-1 for storing user data, and a management extent 202-3for storing management information. The management information, forexample, includes the access attribute of the mainframe volume and soon. The user extent 202-1 can be recognized by the host computer 100 andis allocated to the logical unit 201, whereas the management extent202-3 cannot be recognized by the host computer 100 and is not allocatedto the logical unit 201.

(6) VDEV Consolidation

As shown in FIG. 9, the mapping relation of gathering the storageextents of a plurality of virtual devices 203 and allocating them to onelogical device 202 is referred to as VDEV consolidation.

(7) VDEV Discrete (Basic Form)

As shown in FIG. 10, the mapping relation of gathering the storageextents of a plurality of device groups 204 and allocating them to onevirtual device 203 is referred to as VDEV discrete. The mapping relationof VDEV discrete includes the modified examples 1 and 2 described below.

(8) VDEV Discrete (Modified Example 1)

As one modified example of VDEV discrete, for example, as shown in FIG.11, one device group 204 may be partitioned into a plurality of storageextents, and one virtual device 203 may be allocated to each of thepartitioned storage extents.

(9) VDEV Discrete (Modified Example 2)

As another modified example of VDEV discrete, for example, as shown inFIG. 12, each of the plurality of device groups 204 may be partitionedinto a plurality of storage extents, and each of the partitioned storageextents may be allocated to a plurality of virtual devices 203.

(10) DEVGr/EDEV

With respect to the mapping relation between the device group 204 andthe expansion device 206, for instance, as shown in FIG. 13, all or apart of the respective storage extents of the plurality of expansiondevices 206 may be gathered and allocated to one device group 204. Amongthe expansion devices 206, there may be a storage extent that is notallocated to the device group 204. For example, as shown in FIG. 14, allor a part of the respective storage extents of the plurality ofexpansion devices 206 may be gathered and allocated to a plurality ofdevice groups 204. Among the expansion devices 206, there may be astorage extent that is not allocated to any device group 204. Forexample, as shown in FIG. 15, there may be an expansion device 206 thatis allocated to a plurality of device groups 204, or an expansion device206 that is allocated only to certain device groups 204.

(11) Heterogenous Media Mixed RAID

As shown in FIG. 16, heterogenous devices (for instance, physical device205 and expansion device 206) may be mixed and allocated to the storageextent of one device group 204. For example, as shown in FIG. 17,heterogenous disk drives (for instance, FC disk drive 520 and SATA diskdrive 530) may be mixed and allocated to the storage extent of onedevice group 204. For example, as shown in FIG. 18 to FIG. 20, the flashmemory 540 and the disk drive 550 may be mixed and allocated to thestorage extent of one device group 204.

In FIG. 18, a device group 204 having a RAID 0/1 configuration based ona plurality of flash memories 540 and a plurality of disk drives 550 isconfigured. A data volume is configured with a plurality of flashmemories 540, and a mirror volume is configured with a plurality of diskdrives 550. In this kind of drive configuration, data is read from theflash memory 540 during random reading. Data is read respectively fromthe flash memory 540 and the disk drive 550 during sequential reading.Data is respectively written in the flash memory 540 and the disk drive550 during writing. According to this kind of drive configuration, it ispossible to utilize the high speed of the flash memory 540, and realizelow costs in comparison to a RAID configured with only the flashmemories 540.

In FIG. 19, a device group 204 having a RAID 4 configuration isconfigured from three flash memories 540 and one disk drive 550. Theflash memory 540 stores data and the disk drive 550 stores parity data.In this kind of drive configuration, it is possible to extend the lifespan of the flash memory 540 by not using the flash memory 540, which asa write life, in a parity drive with numerous accesses.

In FIG. 20, a device group 204 having a RAID 4 configuration isconfigured from one flash memory 540 and three disk drives 550. Theflash memory 540 stores data and the disk drive 550 stores parity data.In this kind of drive configuration, it is possible to improve the writeperformance by not using the flash memory 540 in a parity drive withnumerous accesses.

(12) AOU

FIG. 21 shows the mutual mapping relation referred to as AOU between thestorage hierarchies in the storage system 130. The logical unit 201belongs to the LU hierarchy. The AOU volume 202 c and a plurality ofpool volumes 202 d belong to the LDEV hierarchy. A plurality of poolvolumes 203 c belong to the VDEV hierarchy. A plurality of expansiondevices 206 e belong to the PDEV/EDEV hierarchy. The AOU volume 202 c isallocated to the logical unit 201 recognized by the host computer 100. Apart of the respective storage extents of the plurality of pool volumes203 c is allocated to the AOU volume 202 c. It is possible todynamically allocate the storage extent of the pool volume 203 c to theAOU volume 202 c, and the capacity of the AOU volume 202 c can be freelyincreased or decreased. The respective storage extents of the pluralityof expansion devices 206 e are allocated to the respective storageextents of the plurality of pool volumes 203 c. Incidentally, thephysical device may be disposed in substitute for the expansion device206 e in the PDEV/EDEV hierarchy.

(13) Snapshot

FIG. 22 shows the mutual mapping relation between the storagehierarchies in the storage system 130 with a snapshot function. Thelogical unit 201 belongs to the LU hierarchy. The primary volume 202 e,secondary volume 202 f, and a plurality of pool volumes 202 g belong tothe LDEV hierarchy. The virtual device 203 d, and a plurality of poolvolume 203 e belong to the VDEV hierarchy. The expansion devices 206 f,206 g belong to the PDEV/EDEV hierarchy. The logical device 202 e isallocated to the logical unit 201. The virtual device 203 d is allocatedto the logical device 202 e. The expansion device 206 f is allocated tothe virtual device 203 d. The secondary volume 202 f is a virtuallogical volume for restoring the data image of the primary volume 202 eat a certain point in time from the data stored in the primary volume202 e at a certain point in time, and data saved from the primary volume202 e to the pool volume 203 e after a certain point in time.

The host group is now explained with reference to FIG. 23. A pluralityof host computers 100 a, 100 c belonging to the host group of host groupnumber #0 can respectively access the logical device 202 h of logicaldevice number #0 by designating port number #0 as the number of the port131, and designating LUN #0 as the number of the logical unit 201.Meanwhile, the host computer 100 b belonging to the host group of hostgroup number #1 can access the logical device 202 i of logical devicenumber #1 by designating port number #0 as the number of the port 131,and designating LUN #0 as the number of the logical unit 201. Like this,even if a certain host computer 100 designates the same port number andthe same logical unit number, the accessible logical device 202 willdiffer depending on the host group number to which the host computer 100belongs.

In the logical unit migration processing pertaining to this embodiment,when migrating a logical unit 201 available to one host computer 100belonging to a certain host group to another storage system 130, theother host computer 100 belonging to that host group shall also executethe same logical unit migration processing.

The alternate path is now explained with reference to FIG. 24 and FIG.25. As shown in FIG. 24, when there are a plurality of paths 406, 407for connection from the host computer 100 to the logical device 202 j inthe storage system 130 and one path 406 among the plurality of paths406, 407 is set as a preferred path, the other path 407 is set as analternate path. The alternate path is also referred to as a standbypath. The host computer 100 is able to access the logical device 202 jvia the path 406 by designating port number #0 as the number of the port131, and designating LUN #0 as the number of the logical unit 201 c.Further, the host computer 100 is able to access the logical device 202j via the path 407 by designating port number #1 as the number of theport 131, and designating LUN #0 as the number of the logical unit 201d. The link manager 108 executes processing for selecting either thepath 406 or path 407 as the path for accessing the logical device 202 j.Since the logical units 201 c, 201 d are both virtualizations of thesame logical device 202 j, when migrating one logical unit (for example,logical unit 201 c) to another storage system 130, it is necessary tomigrate the other logical unit (for example, logical unit 201 d) toanother storage system 130.

As shown in FIG. 25, when there are a plurality of paths 408, 409 forconnection from the storage system 130 to the logical device 202 k inthe external storage system 150 and one path 408 among the plurality ofpaths 408, 409 is set as a preferred path, the other path 409 is set asan alternate path. The storage system 130 is able to access the logicaldevice 202 k via the path 408 by designating port number #0 as thenumber of the port 151, and designating LUN #0 as the number of thelogical unit 201 e. Further, the storage system 130 is able to accessthe logical device 202 k via the path 409 by designating port number #1as the number of the port 151, and designating LUN #0 as the number ofthe logical unit 201 f. Since the logical units 201 e, 201 f are bothvirtualizations of the same logical device 202 k, when migrating onelogical unit (for example, logical unit 201 e) to another storage system130, it is necessary to migrate the other logical unit (for example,logical unit 201 f) to another storage system 130.

The various types of information used in the logical unit migrationprocessing are now explained with reference to FIG. 26 to FIG. 33.

FIG. 26 shows the host group management information 601. The host groupmanagement information 601 retains information concerning the hostgroup. The host group management information 601 retains informationfrom the entry 701 to the entry 705.

The entry 701 stores the host group number as the identifyinginformation for identifying the host group in the computer system 500.

The entry 702 stores several host computers 100 belonging to the hostgroup specified by the host group number.

The entry 703 stores a list of host names of all host computers 100belonging to the host group specified by the host group number. As thehost name, there is no particular limitation so as long as it isinformation capable of uniquely identifying the host computer 100, and,for instance, a WWN (World Wide Name) assigned to the port 107 may beused.

The entry 704 stores the number of logical units accessible from thehost computer 100 belonging to the host group specified by the hostgroup number.

The entry 705 stores a list of the LU path management information 602described later.

FIG. 27 shows the LU path management information 602. The LU pathmanagement information 602 retains information concerning the number ofeffective LUNs defined in each port 130 regarding the respective ports131 in the storage system 130. The LU path management information 602retains information from the entry 801 to the entry 805.

The entry 801 stores the port number for uniquely identifying the port131 in the storage system 130.

The entry 802 stores information (for example, target ID or LUN) foridentifying the logical unit 201. The target ID and LUN are identifiersfor identifying the logical unit 201. For example, the SCSI-ID and LUNused in accessing the device on a SCSI protocol from the host computer100 are used as identifiers for identifying the logical unit 201.

The entry 803 stores a number (LDEV number) of the logical deviceallocated with a LUN stored in the entry 802. A number of therepresentative logical device 202 among the plurality of logical devices202 allocated to the logical unit 201 in a case where the logical unit201 has a LUSE configuration is stored in the entry 803.

The entry 804 stores the number of host computers 100 accessible to thelogical device specified by the LDEV number stored in the entry 803.

The entry 805 stores a list of host names of all host computers 100accessible to the logical device specified by the LDEV number stored inthe entry 803.

FIG. 28 shows the logical device management information 603. The logicaldevice management information 603 retains information from the entry 901to the entry 918 concerning the respective logical devices 202.

The entry 901 stores the LDEV number for identifying the logical device202.

The entry 902 stores the capacity (size) of the logical device 202specified by the LDEV number.

The entry 903 stores the LDEV type of the logical device 202 specifiedby the LDEV number. The storage system 130 is able to define the logicaldevice 202 of a plurality of device types having different datamanagement units in the disk cache or different storage formats ofdevice management information (existence or format of storing managementinformation in the disk space). The LDEV type shows the device type ofeach logical device 202.

The entry 904 stores the LDEV status of the logical device 202 specifiedby the LDEV number. The LDEV status shows the device status of thelogical device 202. The LDEV status includes “online”, “offline”,“unloaded”, and “blocked”. The “online” status shows that the logicaldevice 202 is operating normally, an LU path is defined in one or moreport 131s, and is accessible from the host computer 100. The “offline”status shows that the logical device 202 is defined and operatingnormally, but is not accessible from the host computer 100 due toreasons such as the LU path being undefined. The “unloaded” status showsthat the logical device 202 is not accessible from the host computer 100due to reasons such as a physical device or an external device not beingallocated to the logical device 202. The “blocked” status shows that afailure occurred in the logical device 202 and is not accessible fromthe host computer 100. Although the initial value of the entry 603 d is“unloaded”, this is updated to “offline” with the logical devicedefinition processing, and further updated to “online” with the LU pathdefinition processing.

The entry 905 stores the LUSE status of the logical device 202 specifiedby the LDEV number. The LUSE status shows whether the logical unit 201has a LUSE configuration, and the LDEV number of the representativelogical device among the plurality of logical devices 202 allocated tothe logical unit 201 in a case where the logical unit 201 has a LUSEconfiguration.

The entry 906 stores the number of consolidated LDEVs. The number ofconsolidated LDEVs shows the number of logical devices 202 allocated tothe logical unit 201 in a case where the logical unit 201 has a LUSEconfiguration.

The entry 907 stores the consolidated LDEV number list. The consolidatedLDEV number list shows a list of the LDEV numbers of the logical device202 allocated to the logical unit 201 in a case where the logical unit201 has a LUSE configuration.

The entry 908 stores the number of LU paths. The LU path is a path forconnecting the host computer 100 to the logical unit 201. The LU pathquantity shows the number of LU paths.

The entry 909 stores a number of the respective host groups, a portnumber for identifying the port 131 accessible from the host computer100 belonging to the host group, and a list of information (target ID orLUN) of the logical unit 201 allocated to the port 131.

The entry 910 stores the number of host computers 100 belonging to therespective host groups.

The entry 911 stores a list of the host names of the host computers 100in a case where access is permitted to one logical unit 201 by aplurality of host computers 100.

The entry 912 stores the number of virtual devices 203 allocated to thelogical device 202 in a case where the logical device 202 has a VDEVconsolidated configuration.

The entry 913 stores a list of the numbers (VDEV numbers) of the virtualdevice 203 in a case where the logical device 202 and the virtual device203 do not correspond one-on-one.

The entry 914 stores information showing the mapping relation betweenthe logical device 202 and the virtual device 203. For example, theentry 914 stores the offset position of the logical device 202 in thevirtual device 203 in a case where the logical device 202 has a CVSconfiguration, and the offset position of the virtual device 203 in thelogical device 202 in a case where the logical device 202 has a VDEVconsolidated configuration.

The entry 915 stores the number of the logical device 202 of the copydestination or migration destination in a case where the logical device202 is being subject to synchronous copy or migration. The entry 915stores an invalid value when the logical device 202 is not being subjectto synchronous copy or migration.

The entry 916 stores information showing the last address completing thedata migration in a case where the logical device 202 is being subjectto data migration (hereinafter referred to as a “data migration progresspointer”). The data migration progress pointer is used for determiningwhether the migration of the storage extent of the access destination iscomplete or incomplete upon the storage system 130 receiving an I/Orequest to the logical device 202 from the host computer 100, andselecting the processing.

The entry 917 stores information showing whether the logical device 202is being subject to synchronous copy, data migration or neitherprocesses (hereinafter referred to as a “synchronous copy/data migrationflag”).

The entry 918 stores an encryption flag. An encryption flag is flaginformation showing whether to encrypt data written in the physicaldevice 205 or the expansion device 206. When the encryption flag is setup as ON, the storage system 130 encrypts the data to be written in thephysical device 205 or the expansion device 206.

FIG. 29 shows the virtual device management information 604. The virtualdevice management information 604 retains information from the entry1001 to the entry 1010 concerning the respective virtual devices 203.

The entry 1001 stores the VDEV number for identifying the virtual device203.

The entry 1002 stores the capacity (size) of the virtual device 203specified by the VDEV number.

The entry 1003 stores the VDEV status of the virtual device 203specified by the VDEV number. The VDEV status shows the device status ofthe virtual device 203. The VDEV status includes “online”, “offline”,“unloaded”, and “blocked”. The LDEV status includes “online”, “offline”,“unloaded”, and “blocked”. The “online” status shows that the virtualdevice 203 is operating normally, and a path is defined from the hostcomputer 100 to the virtual device 203. The “offline” status shows thatthe virtual device 203 is defined and operating normally, but is notaccessible from the host computer 100 due to reasons such as the path tothe virtual device 203 being undefined. The “unloaded” status shows thatthe virtual device 203 is not accessible from the host computer 100 dueto reasons such as a physical device or an external device not beingallocated to the virtual device 203. The “blocked” status shows that afailure occurred in the virtual device 203 and is not accessible fromthe host computer 100. Although the initial value of the entry 1003 is“unloaded”, this is updated to “offline” with the virtual devicedefinition processing, and further updated to “online” with the pathdefinition processing.

The entry 1004 stores the RAID configuration of the virtual device 203specified by the VDEV number. The RAID configuration, for instance,includes the RAID level, data parity quantity, drive configuration,stripe size and so on.

The entry 1005 stores the number of logical devices 202 allocated fromone virtual device 203 in a case where the logical device 202 has a CVSconfiguration.

The entry 1006 stores a list of numbers of the logical devices 202allocated with the virtual device 203 specified by the VDEV number.

The entry 1007 stores a list of information showing the mapping relationbetween the logical device 202 and the virtual device 203. For example,the entry 1007 stores the offset position of the logical device 202 inthe virtual device 203 in a case where the logical device 202 has a CVSconfiguration, and the offset position of the virtual device 203 in thelogical device 202 in a case where the logical device 202 has a VDEVconsolidated configuration.

The entry 1008 stores the number of device groups 204 allocated to thevirtual device 203. For instance, the entry 1008 stores the number ofdevice groups 204 allocated to the virtual device 203 in a case wherethe virtual device 203 has a VDEV discrete configuration. Further, forexample, the entry 1008 is used for allocating a plurality of devicegroups 204 to one virtual device 203 during the logical unit migrationprocessing.

The entry 1009 stores a list of numbers of the device group 204allocated to the virtual device 203.

The entry 1010 stores a list of information showing the mapping relationbetween the virtual device 203 and the device group 204.

FIG. 30 shows the device group management information 605. The devicegroup management information 605 retains information from the entry 1101to the entry 1110 concerning the respective device groups 204.

The entry 1101 stores the device group number for identifying the devicegroup 204.

The entry 1102 stores the capacity (size) of the device group 204specified by the device group number.

The entry 1103 stores the DEVGr status of the device group 204 specifiedby the device group number. The DEVGr status shows the device status ofthe device group 204. DEVGr status includes “online”, “offline”,“unloaded”, and “blocked”. The LDEV status includes “online”, “offline”,“unloaded”, and “blocked”. The “online” status shows that the devicegroup 204 is operating normally, and a path is defined from the hostcomputer 100 to the device group 204. The “offline” status shows thatthe device group 204 is defined and operating normally, but is notaccessible from the host computer 100 due to reasons such as the path tothe device group 204 being undefined. The “unloaded” status shows thatthe device group 204 is not accessible from the host computer 100 due toreasons such as a physical device or an external device not beingallocated to the device group 204. The “blocked” status shows that afailure occurred in the device group 204 and is not accessible from thehost computer 100. Although the initial value of the entry 1103 is“unloaded”, this is updated to “offline” with the device groupdefinition processing, and further updated to “online” with the pathdefinition processing.

The entry 1104 stores the RAID configuration of the device group 204specified by the device group number. The RAID configuration, forinstance, includes the RAID level, data parity quantity, driveconfiguration, stripe size and so on. Nevertheless, when allocating oneexpansion device 206 to one device group 204 such as during the logicalunit migration processing, the RAID configuration is applied to thedevice group 204.

The entry 1105 stores the number of virtual devices 203 allocated to thedevice group 204. When migrating a logical unit 201 having a LUSEconfiguration, since there are cases where a plurality of virtualdevices 203 are allocated to one device group 204, the value of theentry 1105 is updated in such a case.

The entry 1106 stores a list of numbers of the virtual devices 203allocated to the device group 204 specified by the device group number.

The entry 1107 stores a list of information showing the mapping relationbetween the device group 204 and the virtual device 203.

The entry 1108 stores the number of devices (physical devices 205 orexpansion devices 206) allocated to the device group 204.

The entry 1109 stores a list of numbers of devices (physical devices 205or expansion devices 206) allocated to the device group 204.

The entry 1110 stores a list of information showing the mapping relationbetween the device group 204 and the device (physical device 205 orexpansion device 206). For example, the entry 1110 stores the addressand capacity from the top of the expansion device 206 in a case as shownin FIG. 13 to FIG. 15 where only a part of the expansion device 206 isallocated to the device group 204.

FIG. 31 shows the VDEV-DEVGr mapping information 606. The VDEV-DEVGrmapping information 606 retains information from the entry 1201 to theentry 1207.

The entry 1201 stores the number for identifying the VDEV extent. A VDEVextent is a partial extent of the virtual device 203.

The entry 1202 stores the number of device groups 204 associated withthe VDEV extent.

The entry 1203 stores a list of numbers of the device groups 204associated with the VDEV extent.

The entry 1204 stores a list of effective flags. An effective flag isflag information showing whether to execute processing such as mirroringor parity creation to the virtual device 203 allocated to the logicalunit 201. The effective flag is set up as OFF during the logical unitmigration processing, and processing such as mirroring or paritycreation is not performed to the virtual device 203 allocated to thelogical unit 201 of the migration source.

The entry 1205 stores a list of offset addresses of the VDEV extentsassociated with the device group 204.

The entry 1206 stores a list of information showing whether to operatethe respective VDEV extents in the operation mode of cache through read.

The entry 1207 stores a list of information showing whether to operatethe respective VDEV extents in the operation mode of cache throughwrite.

FIG. 32 shows the physical device management information 607. Thephysical device management information 607 retains information from theentry 1301 to the entry 1306 concerning the respective physical devices205 defined in the storage system 130.

The entry 1301 stores the physical device number for identifying thephysical device 205.

The entry 1302 stores the capacity (size) of the physical device 205specified by the physical device number.

The entry 1303 stores the device status of the physical device 205specified by the physical device number. The device status includes“online”, “offline”, “unloaded”, and “blocked”. The “online” statusshows that the physical device 205 is operating normally, and thephysical device 205 is allocated to the logical device 202. The“offline” status shows that the physical device 205 is defined andoperating normally, but the physical device 205 is not allocated to thelogical device 202. The “unloaded” status shows that the physical device205 is not defined in the disk device 137. The “blocked” status showsthat a failure occurred in the physical device 205 and is notaccessible. Although the initial value of the entry 1303 is “unloaded”,this is updated to “offline” with the physical device definitionprocessing, and further updated to “online” when the physical device 205is defined in the logical device 202.

The entry 1304 stores the number of device groups 204 allocated to onephysical device 205 in a case where the storage extent of one physicaldevice 205 is partially allocated to a plurality of device groups 204(refer to FIG. 15).

The entry 1305 stores a list of numbers of the device groups 204allocated to the physical device 205.

The entry 1306 stores information showing the mapping relation betweenthe physical device 205 and the device group 204.

FIG. 33 shows the expansion device management information 608. Theexpansion device management information 608 is for virtualizing theexternal volume 301 of the external storage system 150 as an expansiondevice 206 (internal volume) in the storage system 130. The expansiondevice management information 608 retains information from the entry1401 to the entry 1411 concerning the respective external volumes 301.

The entry 1401 stores an EDEV number for identifying the expansiondevice 206. An EDEV number is an identification number for uniquelyidentifying the external volume 301 in the storage system 130.

The entry 1402 stores the capacity (size) of the expansion device 206specified by the EDEV number.

The entry 1403 stores the device status of the expansion device 206specified by the EDEV number. The device status includes “online”,“offline”, “unloaded”, and “blocked”. The “online” status shows that theexpansion device 206 is operating normally, and the expansion device 206is allocated to the logical device 202. The “offline” status shows thatthe expansion device 206 is defined and operating normally, but theexpansion device 206 is not allocated to the logical device 202. The“unloaded” status shows that the expansion device 206 is not defined.The “blocked” status shows that a failure occurred in the expansiondevice 206 and is not accessible. Although the initial value of theentry 1403 is “unloaded”, this is updated to “offline” with theexpansion device definition processing, and further updated to “online”when the expansion device 206 is defined in the logical device 202.

The entry 1404 stores the number of device groups 204 allocated to oneexpansion device 206 in a case where the storage extent of one expansiondevice 206 is partially allocated to a plurality of device groups 204(refer to FIG. 15).

The entry 1405 stores a list of numbers of the device groups 204allocated to the expansion device 206.

The entry 1406 stores information showing the mapping relation betweenthe expansion device 206 and the device group 204.

The entry 1407 stores storage identifying information for identifyingthe external storage system 150 to virtualize the expansion device 206.As the storage identifying information, for example, a combination ofvendor identifying information for identifying the vendor that ismanufacturing and selling the external storage system 150 and the serialnumber for uniquely allocating the respective vendors may be considered.

The entry 1408 stores an LDEV number of the external volume 301 managedby the external storage system 150.

The entry 1409 stores a port number for identifying the initiator portfor connecting to the external storage system 150 among a plurality ofports 131 in the storage system 130.

The entry 1410 stores a list of port IDs for identifying the ports 151and the target IDs and LUNs for identifying the external volume 301 in acase where the external volume 301 is defined in one or more ports 151in the external storage system 150.

The entry 1411 stores access control information. The access controlinformation is information for managing which storage system 130 has anaccess right for the respective extents of the external volume 301 in acase where the external volume 301 is shared by a plurality of storagesystems 130.

FIG. 34 shows the software configuration of the computer system 500. Thecontrol memory 135 in the storage system 130 stores various types ofconfiguration management information (host group management information601, LU path management information 602, logical device managementinformation 603, virtual device management information 604, device groupmanagement information 605, VDEV-DEVGr mapping information 606, physicaldevice management information 607, expansion device managementinformation 608, and device function management information 609).

The device function management information 609 retains informationshowing the various attributes set in the respective logical devices202. As examples of attribute information of the logical device 202,there are access control information for limiting the access to thelogical device 202 to a specified host computer 100, access attributeinformation for inhibiting the read access or write access to thelogical device 202, and encryption information such as key informationused in determining the encryption of data to be stored in the logicaldevice 202 and decryption of such data.

The memory 133 in the storage system 130 stores the various types ofconfiguration management information described above, as well as astorage I/O processing program 221 and a logical unit migrationprocessing program 222. Details of the storage I/O processing to beexecuted by the storage I/O processing program 221 and details of thelogical unit migration processing program 222 to be executed by thelogical unit migration processing program 222 will be described later.

The memory 112 in the management server 110 stores the various types ofconfiguration management information described above, as well as alogical unit migration command processing program 241 and a storage loadmonitoring program 242. Details of the LU migration command processingto be executed by the logical unit migration command processing program241 and details of the processing to be executed by the storage loadmonitoring program 242 will be described later.

The memory 102 in the host computer 100 stores device path managementinformation 251 and a host I/O processing program 261. The host computer100 confirms the logical device provided by the storage system 130 orthe external storage system 150, and manages the logical device byassociating it with a device file. The device path managementinformation 251 contains information showing the relation between thelogical device and the device file. For example, when the same logicaldevice is allocated to a plurality of ports 131 of the storage system130, a plurality of device files are created from the same logicaldevice. The host computer 100 consolidates the plurality of device filesassociated with the same logical device, and balances the I/O load tothe logical device or controls the path switching during a networkfailure.

Incidentally, in a case when the configuration of the storage system 130is changed or the configuration of the respective components in thestorage system 130 is changed due to a failure or automatic replacementupon receiving a command from the management server 110 or themanagement terminal 140 based on the storage management software or thestorage administrator, one control processor 132 in the storage system130 updates the configuration management information in the controlmemory 135. Further, the control processor 132 notifies another controlprocessor 132, management terminal 140, and management server 110 to theeffect that the configuration management information has been updated asa result of the configuration of the storage system 130 being changed,and updates the all configuration management information stored in theother control memories 135 to the latest information.

Outline of the migration processing of a logical unit having a CVSconfiguration is now explained with reference to FIG. 35.

The storage system 130 a includes logical units 201 a-1, 201 a-2,logical devices 202 a-1, 202 a-2, a virtual device 203 a, and anexpansion device 206 a. The logical unit 201 a-1 is connected to thehost computer 100 via the path 401-1. The logical unit 201 a-2 isconnected to the host computer 100 via the path 401-2. The virtualdevice 203 a is partitioned into a plurality of storage extents 203 a-1,203 a-2. One storage extent 203 a-1 is mapped to the logical unit 202a-1 via the logical device 202 a-1, and the other storage extent 203 a-1is mapped to the logical unit 202 a-1 via the logical device 202 a-1.The respective logical units 201 a-1, 201 a-2 are partialvirtualizations of the virtual device 203 a, and have a CVSconfiguration.

The expansion device 206 a is a virtualization of the external volume301, and is partitioned into a plurality of storage extents 206 a-1, 206a-2. One storage extent 206 a-1 is mapped to the storage extent 203 a-1,and the other storage extent 206 a-2 is mapped to the storage extent 203a-2.

The outline of processing for migrating data of the logical unit 201 a-2(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines a path 405 for externallyconnecting the external volume 301 and the storage system 130 b, andcreates an expansion device 206 b for virtualizing the external volume301 in the storage system 130 b. The expansion device 206 b ispartitioned into a plurality of storage extents 206 b-1, 206 b-2. Thestorage capacity of the expansion device 206 b is equivalent to thestorage capacity of the external volume 301. The storage capacity of thestorage extent 206 b-2 is equivalent to the storage capacity of thelogical unit 201 a-2.(2) The storage system 130 b creates a virtual device 203 b having astorage capacity that is the same as the storage capacity of theexternal volume 301 in the storage system 130 b. The virtual device 203b is partitioned into a plurality of storage extents 203 b-1, 203 b-2.The storage capacity of the storage extent 203 b-2 is equivalent to thestorage capacity of the logical unit 201 a-2.(3) The storage system 130 b defines a path 404 for externallyconnecting the logical unit 201 a-2 and the storage system 130 b, andcreates an expansion device 206 c for virtualizing the logical unit 201a-2 in the storage system 130 b.(4) The storage system 130 b maps the expansion device 206 c to thevirtual device 203 b (more specifically, to the storage extent 203 b-2).(5) The storage system 130 b creates a logical device 202 b having alogical configuration that is the same as the logical configuration ofthe logical device 202 a-2 in the storage system 130 b. The virtualdevice 203 b (more specifically, the storage extent 203 b-2) is mappedto the logical device 202 b.(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a-2 in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Thevirtual device 202 b is mapped to the logical unit 201 b.(7) The host computer 100 switches the path 401-2 to the path 403 as apath for accessing the external volume 301. Here, access from the hostcomputer 100 to the logical unit 201 a-2 is inhibited such as bydeleting the path 401-2. Incidentally, path switching from the path401-2 to the path 403 may also be conducted by the storage systems 130a, 130 b, or the management server 110. Further, it is not necessarilythe case that the path 401-2 needs to be deleted, and, for instance, thepath 401-2 may be set as an alternate path (for instance, a path to beused during system failure) of the path 403, and the path 401-2 may beleft as is with the path 401-2 in an invalid state.

As a result of the foregoing processing, not only is the logical unit201 b a virtualization of the logical unit 201 a-2, it is also a partialvirtualization of the external volume 301. Thus, the data I/O path fromthe host computer 100 to the logical unit 201 a-2 during the logicalunit migration processing will be path 403→storage hierarchy(LU/LDEV/VDEV/EDEV) in the storage system 130 b →path 404→storagehierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130 a →path402→external volume 301.

(8) The storage system 130 a sets the operation mode of the storagesystem 130 a for destaging to the external volume 301 all dirty dataaccumulated in the disk cache of the storage system 130 a to a cachethrough mode. Incidentally, the storage system 130 a may autonomouslyset the operation mode to a cache through mode, or set the operationmode to a cache through mode based on an external command (for instance,from the storage system 130 b, the host computer 100, or the managementserver 110).(9) After destaging all dirty data accumulated in the disk cache of thestorage system 130 a to the external volume 301, the storage system 130b releases the mapping relation between the expansion device 206 c andthe virtual device 203 b, and maps the expansion device 206 b to thevirtual device 203 b. In addition, the storage system 130 b deletes thepath 404.

Incidentally, since a part of the external volume 301 will be shared bya plurality of storage systems 130 a, 130 b in the migration processingof a logical unit having a CVS configuration, it is necessary toexclusively control the external volume 301. The exclusive control ofthe external volume 301 may be executed by the external storage system150, or a plurality of storage systems 130 a, 130 b may coordinate andexecute such exclusive control.

Outline of migration processing of a logical unit having a LUSEconfiguration is now explained with reference to FIG. 36.

The storage system 130 a includes a logical unit 201 a, logical devices202 a-1, 202 a-2, virtual devices 203 a-1, 203 a-2, and expansiondevices 206 a-1, 206 a-2. The logical unit 201 a is connected to thehost computer via the path 401. The logical unit 201 a is a storageextent consolidating a plurality of logical devices 202 a-1, 202 a-2,and has a LUSE configuration. The expansion device 206 a-1 is avirtualization of the external volume 301-1, and is mapped to thevirtual device 203 a-1. The virtual device 203 a-1 is mapped to thelogical device 202 a-1. The expansion device 206 a-2 is a virtualizationof the external volume 301-2, and is mapped to the virtual device 203a-2. The virtual device 203 a-2 is mapped to the logical device 202 a-2.

The outline of processing for migrating data of the logical unit 201 a(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines paths 405-1, 405-2 for externallyconnecting the external volumes 301-1, 301-2 and the storage system 130b, and creates expansion devices 206 b-1, 206 b-2 for virtualizing theexternal volumes 301-1, 301-2 in the storage system 130 b.(2) The storage system 130 b creates a virtual device 203 b-1 having astorage capacity that is the same as the storage capacity of theexternal volume 301-1, and a virtual device 203 b-2 having a storagecapacity that is the same as the storage capacity of the external volume301-2 in the storage system 130 b.(3) The storage system 130 b defines a path 404 for externallyconnecting the logical unit 201 a and the storage system 130 b, andcreates an expansion device 206 c for virtualizing the logical unit 201a in the storage system 130 b. The expansion device 206 c is partitionedinto a plurality of storage extents 206 c-1, 206 c-2.(4) The storage system 130 b maps the expansion device 206 c to thevirtual devices 203 b-1,203 b-2 (more specifically, maps the storageextent 206 c-1 to the virtual device 203 b-1, and maps the storageextent 206 c-2 to the virtual device 203 b-2).(5) The storage system 130 b creates a logical device 202 b-1 having alogical configuration that is the same as the logical configuration ofthe logical device 202 a-1, and a logical device 202 b-2 having alogical configuration that is the same as the logical configuration ofthe logical device 202 a-2 in the storage system 130 b. The virtualdevice 203 b-1 is mapped to the logical device 202 b-1, and the virtualdevice 203 b-2 is mapped to the logical device 202 b-2.(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Thelogical devices 202 b-1, 202 b-2 are mapped to the logical unit 201 b.(7) The host computer 100 switches the path 401 to the path 403 as apath for accessing the external volumes 301-1, 301-2. Here, access fromthe host computer 100 to the logical unit 201 a is inhibited such as bydeleting the path 401. Incidentally, path switching from the path 401 tothe path 403 may also be conducted by the storage systems 130 a, 130 b,or the management server 110. Further, it is not necessarily the casethat the path 401 needs to be deleted, and, for instance, the path 401may be set as an alternate path (for instance, a path to be used duringsystem failure) of the path 403, and the path 401 may be left as is withthe path 401 in an invalid state.

As a result of the foregoing processing, not only is the logical unit201 b a virtualization of the logical unit 201 a, it is also avirtualization of the external volumes 301-1, 301-2. Thus, the data I/Opath from the host computer 100 to the logical unit 201 a during thelogical unit migration processing will be path 403→storage hierarchy(LU/LDEV/VDEV/EDEV) in the storage system 130 b →path 404→storagehierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130 a →paths 402-1,402-2→external volumes 301-1, 301-2.

(8) The storage system 130 a sets the operation mode of the storagesystem 130 a for destaging to the external volumes 301-1, 301-2 alldirty data accumulated in the disk cache of the storage system 130 a toa cache through mode. Incidentally, the storage system 130 a mayautonomously set the operation mode to a cache through mode, or set theoperation mode to a cache through mode based on an external command (forinstance, from the storage system 130 b, the host computer 100, or themanagement server 110).(9) After destaging all dirty data accumulated in the disk cache of thestorage system 130 a to the external volumes 301-1, 301-2, the storagesystem 130 b releases the mapping relation between the expansion device206 c and the virtual devices 203 b-1,203 b-2, maps the expansion device206 b-1 to the virtual device 203 b-1, and maps the expansion device 206b-2 to the virtual device 203 b-2. In addition, the storage system 130 bdeletes the path 404.

Outline of migration processing of a logical unit having an externalvolume RAID configuration is now explained with reference to FIG. 37.

The storage system 130 a includes a logical unit 201 a, a logical device202 a, a virtual device 203 a, and expansion devices 206 a-1, 206 a-2.The logical unit 201 a is connected to the host computer 100 via thepath 401. The logical unit 201 a is configured by applying the RAIDconfiguration to a plurality of external volumes 301-1, 301-2, andvirtualizing the external volumes 301-1, 301-2 into one storage extent.As the RAID configuration to be applied to the plurality of externalvolumes 301-1, 301-2, RAID 1 (mirroring) is illustrated in thisembodiment. In the RAID 1 configuration, the external volume 301-1 is aprimary volume, whereas the external volume 301-2 is a secondary volume(mirror volume). As the RAID configuration to be applied to the externalvolumes 301-1, 301-2, without limitation to RAID 1 described above, RAID0, RAID 5, or RAID 6 may also be used. The expansion device 206 a-1 is avirtualization of the external volume 301-1. The expansion device 206a-2 is a virtualization of the external volume 301-2. The virtual device203 a is configured by applying a RAID configuration to a plurality ofexpansion devices 206 a-1, 206 a-2 and virtualizing the expansiondevices 206 a-1, 206 a-2 into one storage extent. The storage extentcorresponding to the primary volume in the virtual device 203 a ismapped to the logical device 202 a. The logical device 202 a is mappedto the logical unit 201 a.

The outline of processing for migrating data of the logical unit 201 a(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines paths 405-1, 405-2 for externallyconnecting the external volumes 301-1, 301-2 and the storage system 130b, and creates expansion devices 206 b-1, 206 b-2 for virtualizing theexternal volumes 301-1, 301-2 in the storage system 130 b.(2) The storage system 130 b creates a virtual device 203 b forvirtualizing the plurality of external volumes 301-1, 301-2 in thestorage system 130 b. When employing mirroring as the RAID configurationfor virtualizing the plurality of external volumes 301-1, 301-2, thestorage capacity of the virtual device 203 b is equivalent to the totalstorage capacity of the plurality of external volumes 301-1, 301-2.(3) The storage system 130 b defines a path 404 for externallyconnecting the logical unit 201 a and the storage system 130 b, andcreates an expansion device 206 c for virtualizing the logical unit 201a in the storage system 130 b.(4) The storage system 130 b maps the expansion device 206 c to thevirtual devices 203 b (more specifically, to the storage extentcorresponding to the primary volume in the virtual device 203 b).(5) The storage system 130 b creates a logical device 202 b having alogical configuration that is the same as the logical configuration ofthe logical device 202 a in the storage system 130 b. The storage extentcorresponding to the primary volume in the virtual device 203 b ismapped to the logical device 202 b.(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Thelogical device 202 is mapped to the logical unit 201 b.(7) The host computer 100 switches the path 401 to the path 403 as apath for accessing the external volumes 301-1, 301-2. Here, access fromthe host computer 100 to the logical unit 201 a is inhibited such as bydeleting the path 401. Incidentally, path switching from the path 401 tothe path 403 may also be conducted by the storage systems 130 a, 130 b,or the management server 110. Further, it is not necessarily the casethat the path 401 needs to be deleted, and, for instance, the path 401may be set as an alternate path (for instance, a path to be used duringsystem failure) of the path 403, and the path 401 may be left as is withthe path 401 in an invalid state.

As a result of the foregoing processing, not only is the logical unit201 b a virtualization of the logical unit 201 a, it is also avirtualization of the external volumes 301-1, 301-2. Thus, the data I/Opath from the host computer 100 to the logical unit 201 a during thelogical unit migration processing will be path 403→storage hierarchy(LU/LDEV/VDEV/EDEV) in the storage system 130 b →path 404→storagehierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130 a →paths 402-1,402-2→external volumes 301-1, 301-2.

(8) The storage system 130 a sets the operation mode of the storagesystem 130 a for destaging to the external volumes 301-1, 301-2 alldirty data accumulated in the disk cache of the storage system 130 a toa cache through mode. Incidentally, the storage system 130 a mayautonomously set the operation mode to a cache through mode, or set theoperation mode to a cache through mode based on an external command (forinstance, from the storage system 130 b, the host computer 100, or themanagement server 110).(9) After destaging all dirty data accumulated in the disk cache of thestorage system 130 a to the external volumes 301-1, 301-2, the storagesystem 130 b releases the mapping relation between the expansion device206 c and the virtual device 203 b, and maps the expansion devices 206b-1, 206 b-2 to the virtual device 203 b. In addition, the storagesystem 130 b deletes the path 404.

Outline of migration processing of the VMA volume is now explained withreference to FIG. 38.

The storage system 130 a includes a logical unit 201 a, a logical device202 a, a virtual device 203 a, and an expansion device 206 a. Thelogical unit 201 a is connected to the host computer 100 via the path401. The logical device 202 a is a VMA volume, and includes a userextent 202 a-1 that is accessible from the host computer 100, and amanagement extent 202 a-2 for storing management information. Managementinformation, for instance, includes access attributes of the VMA volume.The user extent 202 a-1 can be recognized by the host computer 100 bybeing allocated to the logical unit 201 a. The management extent 202 a-2is not allocated to the logical unit 201 a, and cannot be recognized bythe host computer 100. The virtual device 203 a has a user extent 203a-1 that is accessible from the host computer 100, and a managementextent 203 a-2 for storing management information. The expansion device206 a has a user extent 206 a-1 that is accessible from the hostcomputer 100, and a management extent 206 a-2 for storing managementinformation. The user extent 206 a-1 in the expansion device 206 a is avirtualization of the user extent 301-1 in the external volume 301. Themanagement extent 206 a-2 in the expansion device 206 a is avirtualization of the management extent 301-2 in the external volume301. The user extent 206 a-1 is mapped to the user extent 203 a-1. Themanagement extent 206 a-2 is mapped to the management extent 203 a-2.The user extent 203 a-1 is mapped to the user extent 202 a-1. Themanagement extent 203 a-2 is mapped to the management extent 202 a-2.

Incidentally, when the migration source storage system 130 a is notstoring management information in the external volume 301, and isstoring management information in a disk cache or another memory in thestorage system 130 a, it is necessary to destage the managementinformation to the external volume 301 as a prearrangement in executingthe migration processing of the logical unit 201 a.

The outline of processing for migrating data of the logical unit 201 a(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines a path 405 for externallyconnecting the external volume 301 and the storage system 130 b, andcreates an expansion device 206 b for virtualizing the external volume301 in the storage system 130 b. The expansion device 206 b includes auser extent 206 b-1 that is accessible from the host computer 100, and amanagement extent 206 b-2 for storing management information. Thestorage system 130 b maps the management extent 301-2 to the managementextent 206 b-2.(2) The storage system 130 b creates a virtual device 203 b forvirtualizing the external volume 301 in the storage system 130 b. Thevirtual device 203 b has a user extent 203 b-1 that is accessible fromthe host computer 100, and a management extent 203 b-2 for storingmanagement information. The storage system 130 b maps the managementextent 206 b-2 to the management extent 203 b-2.(3) The storage system 130 b defines a path 404 for externallyconnecting the logical unit 201 a and the storage system 130 b, andcreates an expansion device 206 c for virtualizing the logical unit 201a in the storage system 130 b.(4) The storage system 130 b maps the expansion device 206 c to the userextent 203 b-1 in the virtual device 203 b.(5) The storage system 130 b creates a logical device 202 b having alogical configuration that is the same as the logical configuration ofthe logical device 202 a in the storage system 130 b. The logical device202 b has a user extent 202 b-1 that is accessible from the hostcomputer 100, and a management extent 202 b-2 for storing managementinformation. The user extent 203 b-1 is mapped to the user extent 202b-1. The management extent 203 b-2 is mapped to the management extent202 b-2.(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Theuser extent 202 b-1 is mapped to the logical unit 201 b.(7) The host computer 100 switches the path 401 to the path 403 as apath for accessing the external volume 301. Here, access from the hostcomputer 100 to the logical unit 201 a is inhibited such as by deletingthe path 401. Incidentally, path switching from the path 401 to the path403 may also be conducted by the storage systems 130 a, 130 b, or themanagement server 110. Further, it is not necessarily the case that thepath 401 needs to be deleted, and, for instance, the path 401 may be setas an alternate path (for instance, a path to be used during systemfailure) of the path 403, and the path 401 may be left as is with thepath 401 in an invalid state.

As a result of the foregoing processing, not only is the logical unit201 b a virtualization of the logical unit 201 a, it is also avirtualization of the user extent 301-1 in the external volume 301.Thus, the data I/O path from the host computer 100 to the logical unit201 a during the logical unit migration processing will be path403→storage hierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130 b→path 404→storage hierarchy (LU/LDEV/VDEV/EDEV) in the storage system130 a →path 402→external volume 301.

Incidentally, since the storage system 130 b is virtualizing themanagement extent 301-2 in the external volume 130 with the virtualdevice 203 b, it is able to refer to the management information via thepath 405. In order for the storage system 130 a to refer to themanagement information in the external volume 130 via the path 402during the migration processing of the logical unit 201 a, it isnecessary to set the writing from the management extent 203 b-2 in thevirtual device 203 b to the management extent 301-2 in the externalvolume 301 to a cache through mode, and to constantly update themanagement information in the management extent 301-2. Update of themanagement information written in the management extent 301-2 in theexternal volume 301 is conducted by the migration target storage system130 b.

(8) The storage system 130 a sets the operation mode of the storagesystem 130 a for destaging to the external volume 301 all dirty dataaccumulated in the disk cache of the storage system 130 a to a cachethrough mode. Incidentally, the storage system 130 a may autonomouslyset the operation mode to a cache through mode, or set the operationmode to a cache through mode based on an external command (for instance,from the storage system 130 b, the host computer 100, or the managementserver 110).(9) After destaging all dirty data accumulated in the disk cache of thestorage system 130 a to the external volume 301, the storage system 130b releases the mapping relation between the expansion device 206 c andthe virtual device 203 b, and maps the user extent 206 b-1 in theexpansion device 206 b to the user extent 203 b-1 in the virtual device203 b. In addition, the storage system 130 b deletes the path 404.

Incidentally, the method shown in FIG. 38 is not limited to a case wherethe external volume 301 is a VMA volume, and it is possible to migratethe logical unit 201 a via the foregoing processing routine of (1) to(9) even when the external volume 301 is a mainframe volume.

Another method of migration processing of the VMA volume is nowexplained with reference to FIG. 39.

The storage system 130 a includes logical units 201 a-1, 202 a-1, alogical device 202 a, a virtual device 203 a, and an expansion device206 a. The logical unit 201 a-1 is connected to the host computer 100via the path 401, and is recognizable from the host computer 100.Meanwhile, the logical unit 201 a-2 is not connected to the hostcomputer 100, and cannot be recognized from the host computer 100. Thelogical unit 201 a-2 is temporarily created while migrating the logicalunit 201 a-1 from the storage system 130 a to the storage system 130 b.The logical device 202 a is a VMA volume, and has a user extent 202 a-1that is accessible from the host computer 100, and a management extent202 a-2 for storing management information. Management information, forinstance, includes access attributes of the VMA volume. The user extent202 a-1 can be recognized by the host computer 100 by being allocated tothe logical unit 201 a. The management extent 202 a-2 is allocated tothe logical unit 201 a-2, and cannot be recognized by the host computer100. The virtual device 203 a has a user extent 203 a-1 that isaccessible from the host computer 100, and a management extent 203 a-2for storing management information. The expansion device 206 a has auser extent 206 a-1 that is accessible from the host computer 100, and amanagement extent 206 a-2 for storing management information. The userextent 206 a-1 in the expansion device 206 a is a virtualization of theuser extent 301-1 in the external volume 301. The management extent 206a-2 in the expansion device 206 a is a virtualization of the managementextent 301-2 in the external volume 301. The user extent 206 a-1 ismapped to the user extent 203 a-1. The management extent 206 a-2 ismapped to the management extent 203 a-2. The user extent 203 a-1 ismapped to the user extent 202 a-1. The management extent 203 a-2 ismapped to the management extent 202 a-2.

The outline of processing for migrating data of the logical unit 201 a(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines a path 405 for externallyconnecting the external volume 301 and the storage system 130 b, andcreates an expansion device 206 b for virtualizing the external volume301 in the storage system 130 b. The expansion device 206 b includes auser extent 206 b-1 that is accessible from the host computer 100, and amanagement extent 206 b-2 for storing management information.(2) The storage system 130 b creates a virtual device 203 b forvirtualizing the external volume 301 in the storage system 130 b. Thevirtual device 203 b has a user extent 203 b-1 that is accessible fromthe host computer 100, and a management extent 203 b-2 for storingmanagement information.(3) The storage system 130 b defines a path 404-1 for externallyconnecting the logical unit 201 a-1 and the storage system 130 b,defines a path 404-2 for externally connecting the logical unit 201 a-2and the storage system 130 b, creates an expansion device 206 c-1 forvirtualizing the logical unit 201 a-1, and creates an expansion device206 c-2 for virtualizing the logical unit 201 a-2 in the storage system130 b.(4) The storage system 130 b maps the expansion device 206 c-1 to theuser extent 203 b-1 in the virtual device 203 b, and maps the expansiondevice 206 c-2 to the management extent 203 b-2 in the virtual device203 b.(5) The storage system 130 b creates a logical device 202 b having alogical configuration that is the same as the logical configuration ofthe logical device 202 a in the storage system 130 b. The logical device202 b has a user extent 202 b-1 that is accessible from the hostcomputer 100, and a management extent 202 b-2 for storing managementinformation. The user extent 203 b-1 is mapped to the user extent 202b-1. The management extent 203 b-2 is mapped to the management extent202 b-2.(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a-1 in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Theuser extent 202 b-1 is mapped to the logical unit 201 b.(7) The host computer 100 switches the path 401 to the path 403 as apath for accessing the external volume 301. Here, access from the hostcomputer 100 to the logical unit 201 a-1 is inhibited such as bydeleting the path 401. Incidentally, path switching from the path 401 tothe path 403 may also be conducted by the storage systems 130 a, 130 b,or the management server 110. Further, it is not necessarily the casethat the path 401 needs to be deleted, and, for instance, the path 401may be set as an alternate path (for instance, a path to be used duringsystem failure) of the path 403, and the path 401 may be left as is withthe path 401 in an invalid state.

As a result of the foregoing processing, not only is the logical unit201 b a virtualization of the logical unit 201 a-1, it is also avirtualization of the user extent 301-1 in the external volume 301.Thus, the data I/O path from the host computer 100 to the logical unit201 a during the logical unit migration processing will be path403→storage hierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130b→path 404-1→storage hierarchy (LU/LDEV/VDEV/EDEV) in the storage system130 a→path 402→external volume 301.

Incidentally, since the storage system 130 a is virtualizing themanagement extent 301-1 in the external volume 130 with the virtualdevice 203 a-1, it is able to refer to the management information viathe path 402. In order for the storage system 130 b to refer to themanagement information in the external volume 130 during the migrationprocessing of the logical unit 201 a, it merely needs to access themanagement extent 301-2 in the external volume 130 via the path 404-2and the logical unit 201 a-2. Update of the management informationwritten in the management extent 301-2 in the external volume 301 isconducted by the migration target storage system 130 a.

(8) The storage system 130 a sets the operation mode of the storagesystem 130 a for destaging to the external volume 301 all dirty dataaccumulated in the disk cache of the storage system 130 a to a cachethrough mode. Incidentally, the storage system 130 a may autonomouslyset the operation mode to a cache through mode, or set the operationmode to a cache through mode based on an external command (for instance,from the storage system 130 b, the host computer 100, or the managementserver 110).(9) After destaging all dirty data accumulated in the disk cache of thestorage system 130 a to the external volume 301, the storage system 130b releases the mapping relation between the expansion device 206 c-1 andthe user extent 203 b-1, and releases the mapping relation between theexpansion device 206 c-2 and the management extent 203 b-2. The storagesystem 130 b further maps the user extent 206 b-1 in the expansiondevice 206 b to the user extent 203 b-1, and maps the management extent206 b-2 to the management extent 203 b-2. In addition, the storagesystem 130 b deletes the path 404.

Incidentally, the method shown in FIG. 39 is not limited to a case wherethe external volume 301 is a VMA volume, and it is possible to migratethe logical unit 201 a-1 via the foregoing processing routine of (1) to(9) even when the external volume 301 is a mainframe volume.

The primary difference between the method shown in FIG. 38 and themethod shown in FIG. 39 is as follows. With the method shown in FIG. 39,the migration target storage system 130 b accesses the management extent301-2 via the migration source storage system 130 a, whereas with themethod shown in FIG. 38, the migration target storage system 130 bdirectly accesses the management extent 301-2. With the method shown inFIG. 39, the update of management information in the management extent301-2 is executed by the migration source storage system 130 a, whereasthe with the method shown FIG. 38, the update of management informationin the management extent 301-2 is executed by the migration targetstorage system 130 b.

Another method of migration processing of the VMA volume is nowexplained with reference to FIG. 40.

The storage system 130 a includes logical units 201 a, 201 a′, a logicaldevice 202 a, a virtual device 203 a, and an expansion device 206 a. Thelogical unit 201 a is connected to the host computer 100 via the path401, and is recognizable from the host computer 100. Meanwhile, thelogical unit 201 a′ is not connected to the host computer 100, andcannot be recognized from the host computer 100. The logical unit 201 a′is temporarily created while migrating the logical unit 201 a from thestorage system 130 a to the storage system 130 b. The logical unit 201a′ has a user extent 201 a-1′ and a management extent 201 a-2′. Thelogical device 202 a is a VMA volume, and has a user extent 202 a-1 thatis accessible from the host computer 100, and a management extent 202a-2 for storing management information. Management information, forinstance, includes access attributes of the VMA volume. The user extent202 a-1 can be recognized by the host computer 100 by being allocated tothe logical unit 201 a. The user extent 202 a-1 is also allocated to theuser extent 201 a-1′ in the logical unit 201 a′. The management extent202 a-2 is allocated to the management extent 201 a-2′ in the logicalunit 201 a′. The virtual device 203 a has a user extent 203 a-1 that isaccessible from the host computer 100, and a management extent 203 a-2for storing management information. The expansion device 206 a has auser extent 206 a-1 that is accessible from the host computer 100, and amanagement extent 206 a-2 for storing management information. The userextent 206 a-1 in the expansion device 206 a is a virtualization of theuser extent 301-1 in the external volume 301. The management extent 206a-2 in the expansion device 206 a is a virtualization of the managementextent 301-2 in the external volume 301. The user extent 206 a-1 ismapped to the user extent 203 a-1. The management extent 206 a-2 ismapped to the management extent 203 a-2. The user extent 203 a-1 ismapped to the user extent 202 a-1. The management extent 203 a-2 ismapped to the management extent 202 a-2.

The outline of processing for migrating data of the logical unit 201 a(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines a path 405 for externallyconnecting the external volume 301 and the storage system 130 b, andcreates an expansion device 206 b for virtualizing the external volume301 in the storage system 130 b. The expansion device 206 b includes auser extent 206 b-1 that is accessible from the host computer 100, and amanagement extent 206 b-2 for storing management information.(2) The storage system 130 b creates a virtual device 203 b forvirtualizing the external volume 301 in the storage system 130 b. Thevirtual device 203 b has a user extent 203 b-1 that is accessible fromthe host computer 100, and a management extent 203 b-2 for storingmanagement information.(3) The storage system 130 b defines a path 404 for externallyconnecting the logical unit 201 a′ and the storage system 130 b, andcreates an expansion device 206 c for virtualizing the logical unit 201a′ in the storage system 130 b. The expansion device 206 c has a userextent 206 c-1 that is accessible from the host computer 100, and amanagement extent 206 c-2 for storing management information.(4) The storage system 130 b maps the user extent 206 c-1 in theexpansion device 206 c-1 to the user extent 203 b-1 in the virtualdevice 203 b, and maps the management extent 206 c-2 in the expansiondevice 206 c-2 to the management extent 203 b-2 in the virtual device203 b.(5) The storage system 130 b creates a logical device 202 b having alogical configuration that is the same as the logical configuration ofthe logical device 202 a in the storage system 130 b. The logical device202 b has a user extent 202 b-1 that is accessible from the hostcomputer 100, and a management extent 202 b-2 for storing managementinformation. The user extent 203 b-1 is mapped to the user extent 202b-1. The management extent 203 b-2 is mapped to the management extent202 b-2.(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Theuser extent 202 b-1 is mapped to the logical unit 201 b.(7) The host computer 100 switches the path 401 to the path 403 as apath for accessing the external volume 301. Here, access from the hostcomputer 100 to the logical unit 201 a-1 is inhibited such as bydeleting the path 401. Incidentally, path switching from the path 401 tothe path 403 may also be conducted by the storage systems 130 a, 130 b,or the management server 110. Further, it is not necessarily the casethat the path 401 needs to be deleted, and, for instance, the path 401may be set as an alternate path (for instance, a path to be used duringsystem failure) of the path 403, and the path 401 may be left as is withthe path 401 in an invalid state.

As a result of the foregoing processing, not only is the logical unit201 b a virtualization of the logical unit 201 a, it is also avirtualization of the user extent 301-1 in the external volume 301.Thus, the data I/O path from the host computer 100 to the logical unit201 a during the logical unit migration processing will be path403→storage hierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130b→path 404→storage hierarchy (LU/LDEV/VDEV/EDEV) in the storage system130 a→path 402→external volume 301.

Incidentally, since the storage system 130 a is virtualizing themanagement extent 301-1 in the external volume 130 with the virtualdevice 203 a-1, it is able to refer to the management information viathe path 402. In order for the storage system 130 b to refer to themanagement information in the external volume 130 during the migrationprocessing of the logical unit 201 a, it merely needs to access themanagement extent 301-2 in the external volume 130 via the path 404 andthe logical unit 201 a′. Update of the management information written inthe management extent 301-2 in the external volume 301 is conducted bythe migration target storage system 130 a.

(8) The storage system 130 a sets the operation mode of the storagesystem 130 a for destaging to the external volume 301 all dirty dataaccumulated in the disk cache of the storage system 130 a to a cachethrough mode. Incidentally, the storage system 130 a may autonomouslyset the operation mode to a cache through mode, or set the operationmode to a cache through mode based on an external command (for instance,from the storage system 130 b, the host computer 100, or the managementserver 110).(9) After destaging all dirty data accumulated in the disk cache of thestorage system 130 a to the external volume 301, the storage system 130b releases the mapping relation between the expansion device 206 c andthe virtual device 203 b, and maps the expansion device 206 c to thevirtual device 203 b. More specifically, the storage system 130 b mapsthe user extent 206 b-1 in the expansion device 206 b to the user extent203 b-1 in the virtual device 203 b, and maps the management extent 206b-2 in the expansion device 206 b to the management extent 203 b-2 inthe virtual device 203 b. In addition, the storage system 130 b deletesthe path 404.

Outline of processing for migrating a plurality of logical units is nowexplained with reference to FIG. 41.

The storage system 130 a includes a plurality of logical units 201 a-1,201 a-2, a plurality of logical devices 202 a-1, 202 a-2, a plurality ofvirtual devices 203 a-1, 203 a-2, and a plurality of expansion devices206 a-1, 206 a-2. The expansion device 206 a-1 is a virtualization ofthe external volume 301-1, and is connected to the external storagesystem 150 via the path 402-1. The expansion device 206 a-1 is mapped tothe virtual device 203 a-1. The virtual device 203 a-1 is mapped to thelogical device 202 a-1. The logical device 202 a-1 is mapped to thelogical unit 201 a-1. The logical unit 201 a-1 is a virtualization ofthe external volume 301-1, and is connected to the host computer 100 viathe path 401-1.

Meanwhile, the expansion device 206 a-2 is a virtualization of theexternal volume 301-2, and is connected to the external storage system150 via the path 402-2. The expansion device 206 a-2 is mapped to thevirtual device 203 a-2. The virtual device 203 a-2 is mapped to thelogical device 202 a-2. The logical device 202 a-2 is mapped to thelogical unit 201 a-2. The logical unit 201 a-2 is a virtualization ofthe external volume 301-2, and is connected to the host computer 100 viathe path 401-2.

Now, in order to migrate a plurality of logical units 201 a-1, 201 a-2from the storage system 130 a to the storage system 130 b in theforegoing configuration, as with the processing routines describedabove, the storage system 130 b creates a plurality of logical units 201b-1, 201 b-2 to be migrated. The logical unit 201 b-1 is connected tothe host computer via the path 403-1. The logical unit 201 b-2 isconnected to the host computer 100 via the path 403-2. In addition, thestorage system 130 b creates a plurality of expansion devices 206 c-1,206 c-2, a plurality of virtual devices 203 b-1, 203 b-2, and aplurality of logical devices 202 b-1, 202 b-2 for virtualizing theplurality of logical units 201 a-1, 201 a-2 of the migration source. Theexpansion device 206 c-1 virtualizes the logical unit 201 a-1 during themigration processing of the logical unit 201 a-1 on the one hand, andconnects to the external volume 301-1 via the path 405-1 and virtualizesthe external volume 301-1 after the migration processing of the logicalunit 201 a-1 (more specifically, after completing the destaging of dirtydata written in the virtual device 203 a-1). The expansion device 206c-2 virtualizes the logical unit 201 a-2 during the migration processingof the logical unit 201 a-2 on the one hand, and connects to the logicalunit 201 a-2 via the path 405-2 and virtualizes the external volume301-2 after the migration processing of the logical unit 201 a-2 (morespecifically, after completing the destaging of dirty data written inthe virtual device 203 a-2).

Incidentally, a command for migrating a plurality of logical units maybe given from the management server 110 (refer to FIG. 2) to therespective storage systems 130 a, 130 b, or from the host computer 100to the respective storage systems 130 a, 130 b.

Details regarding the logical unit migration processing are nowexplained with reference to FIG. 42 to FIG. 46.

FIG. 42 shows the logical unit migration command processing routine. Thelogical unit migration command processing routine is executed with thelogical unit migration command processing program 241 in the managementserver 110.

The management server 110 gives a command to the storage system 130 a(migration source storage) and the storage system 130 b (migrationdestination storage) for migrating one or more logical units (step4201). Here, the storage administrator operating the management server110 may give the logical unit migration command to the respectivestorage systems 130 a, 130 b, or the management software in themanagement server 110 may give the logical unit migration command to therespective storage systems 130 a, 130 b. Incidentally, the logical unitmigration command may also be given from the host computer 100 to therespective storage systems 130 a, 130 b.

When the respective storage systems 130 a, 130 b receive the logicalunit migration command, they execute processing for migrating thedesignated logical units (step 4202).

When the migration of certain logical units among all designated logicalunits is incomplete (step 4203; NO), the respective storage systems 130a, 130 b execute the logical unit migration processing (step 4202).

When the migration of all designated logical units is complete (step4203; YES), the respective storage systems 130 a, 130 b issue amigration completion report to the management server 110 (step 4204).Incidentally, when the logical unit migration command is given from thehost computer 100 to the respective storage systems 130 a, 130 b, therespective storage systems 130 a, 130 b issue a migration completionreport to the host computer 100.

FIG. 43 shows the logical unit migration processing subroutine. Thelogical unit migration processing subroutine is executed with thelogical unit migration processing program 222 in the storage system 130.

When the logical unit migration processing subroutine is activated, therespective storage systems 130 a, 130 b execute the migration targetselection processing (step 4301), the migration preparation processing(step 4302), and the migration processing (step 4303).

FIG. 44 shows the migration target selection processing subroutine. Whenthe migration target selection processing subroutine is activated, thestorage system 130 a selects a logical device (logical device to bemigrated) corresponding to the logical unit to be migrated (step 4401).For instance, in a LUSE configuration, a plurality of logical devicesare selected for one logical unit.

Subsequently, the storage system 130 a selects all host computers 100 touse the logical device to be migrated (step 4402). For example, inaddition to the host computers 100 belonging to the same host group, thehost computers 100 belonging to other host groups are also selected.

The storage system 130 a thereafter selects a VDEV extent (VDEV extentto be migrated) corresponding to the logical device to be migrated (step4403). The VDEV extent may correspond to a part of one virtual device,or may correspond to a plurality of virtual devices. For example, in aCVS configuration, a part of the virtual device is selected as the VDEVextent corresponding to the logical device to be migrated. Meanwhile, ina VDEV consolidated configuration, a plurality of virtual devices areselected as the VDEV extent corresponding to the logical device to bemigrated.

Subsequently, the storage system 130 a selects a device group (devicegroup to be migrated) corresponding to the VDEV extent to be migrated(step 4404). The device group may correspond to a part of one VDEVextent, or may correspond to a plurality of VDEV extents. For example,in a VDEV discrete configuration, a plurality of device groups areselected as the device group corresponding to the VDEV extent to bemigrated.

The storage system 130 a thereafter selects an expansion device(expansion device to be migrated) corresponding to the device group tobe migrated (step 4405). The expansion device may correspond to a partof one device group, or may correspond to a plurality of device groups.For example, when certain storage extents of one expansion device areallocated to a certain device group, and the remaining storage extentsare allocated to another device group, a part of the expansion device isselected as the expansion device corresponding to the device group to bemigrated. Meanwhile, in an external volume RAID configuration, aplurality of expansion devices are selected as the expansion devicecorresponding to the device group to be migrated.

Subsequently, the storage system 130 a selects an external volumecorresponding to the expansion device to be migrated (step 4406).

As a result of the foregoing processing, it is possible to respectivelyselect a logical device corresponding to the logical unit to bemigrated, a virtual device corresponding to such logical device, adevice group corresponding to such virtual device, an expansion devicecorresponding to such device group, and an external volume correspondingto such expansion device.

FIG. 45 shows the migration preparation processing subroutine. When themigration preparation processing subroutine is activated, the storagesystem 130 a sets an access permit from the storage system 130 b to theexternal volume (step 4501).

The storage system 130 b defines a path for connecting from the storagesystem 130 b to the external volume, and creates a first expansiondevice (corresponds to the expansion device 206 b in FIG. 1) forvirtualizing the external volume in the storage system 130 b (step4502).

The storage system 130 b associates the first expansion device in thestorage system 130 b with the device group in the storage system 130 b(step 4503). For example, in an external volume RAID configuration, aplurality of first expansion devices are associated with one devicegroup.

The storage system 130 b associates the device group, which isassociated with the first expansion device in the storage system 130 b,with the virtual device in the storage system 130 b (step 4504).

The storage system 130 a sets an access permit from the storage system130 b to the migration source logical unit in the storage system 130 a(step 4505).

The storage system 130 b associates a second expansion device(corresponding to the expansion device 206 c of FIG. 1) in the storagesystem 130 b with the logical unit to become the migration target in thestorage system 130 a (step 4506).

For example, when the logical unit to be migrated has an external volumeRAID configuration, the second expansion device in the storage system130 b is associated with a part (excluding the storage extents storingparity data and mirror data) of the virtual device in the storage system130 a.

For example, when the logical unit to be migrated has a CVSconfiguration, the second expansion device in the storage system 130 bis associated with a part of the virtual device in the storage system130 a.

For example, when the logical unit to be migrated has a LUSEconfiguration, the second expansion device in the storage system 130 bis associated with a plurality of virtual devices in the storage system130 a.

For example, when the logical unit to be migrated is a VMA volume, thesecond expansion device in the storage system 130 b is associated with apart (user extent) of the virtual device in the storage system 130 a.

The storage system 130 b associates the second expansion device in thestorage system 130 b with the device group in the storage system 130 b(step 4507).

The storage system 130 b associates the device group, which isassociated with the second expansion device in the storage system 130 b,with the virtual device in the storage system 130 b (step 4508).

For example, when the logical unit to be migrated has an external volumeRAID configuration, the second expansion device in the storage system130 b is associated with a part (excluding the storage extents storingparity data and mirror data) of the virtual device in the storage system130 b.

For example, when the logical unit to be migrated has a CVSconfiguration, the second expansion device in the storage system 130 bis associated with a part of the virtual device in the storage system130 b.

For example, when the logical unit to be migrated has a LUSEconfiguration, the second expansion device in the storage system 130 bis associated with a plurality of virtual devices in the storage system130 b.

For example, when the logical unit to be migrated is a VMA volume, thesecond expansion device in the storage system 130 b is associated with apart (user extent) of the virtual device in the storage system 130 b.

The storage system 130 b invalidates the mapping relation between thedevice group in the storage system 130 b associated with the firstexpansion device and the virtual device in the storage system 130 b, andactivates the mapping relation between the device group in the storagesystem 130 b associated with the second expansion device and the virtualdevice in the storage system 130 b (step 4509).

The storage system 130 b sets the operation mode of the storage system130 b to a cache through mode, and sets the operation mode of thestorage system 130 a to a write after mode (step 4510).

The storage system 130 b creates a logical unit to be migrated in thestorage system 130 b (step 4511).

The storage system 130 b sets access attributes to the logical unit tobe migrated (step 4512). As the access attributes, for instance, thereare settings relating to the host group and settings relating to thealternate path.

The storage system 130 b releases the function of encrypting datawritten from the storage system 130 b into the external volume (step4513). Data written in the external volume during the logical unitmigration processing is encrypted with the migration source storagesystem 130 a.

The storage system 130 b defines a path for connecting the logical unitto be migrated and the host computer 100 (step 4514). When there are aplurality of logical units to be migrated, a path is defined forconnecting the respective logical units to be migrated and the hostcomputer 100.

The storage system 130 b makes the host computer 100 recognize thelogical unit to be migrated (step 4515). When there are a plurality ofhost computers 100 to use the logical unit to be migrated, therespective host computers 100 are made to recognize the logical unit tobe migrated.

The storage system 130 b sets a path for connecting the logical unit tobe migrated and the host computer 100 as an alternate path of a path forconnecting the migration source logical unit and the host computer 100(step 4516).

FIG. 46 shows the migration processing subroutine. When the migrationprocessing subroutine is activated, the host computer 100 halts the I/Orequest of the migration source logical unit (step 4601). The storagesystem 130 a may also inhibit the I/O request from the host computer100. When there are a plurality of host computers 100 using themigration source logical unit, the I/O request from the respective hostcomputers 100 to the migration source logical unit is halted orinhibited.

The host computer 100 switches the path for connecting to the migrationsource logical unit to the path for connecting to the logical unit to bemigrated, and deletes the path for connecting to the migration sourcelogical unit (step 4602). When there are a plurality of host computers100 using the migration source logical unit, the respective hostcomputers 100 simultaneously execute path switching.

The migration source storage system 130 a inhibits the access from thehost computer 100 (step 4603).

The migration target storage system 130 b releases the cache throughmode as the operation mode of the storage system 130 b, and sets theoperation mode to the write after mode (step 4604).

The migration source storage system 130 a releases the write after modeas the operation mode of the storage system 130 a, and sets theoperation mode to the cache through mode (step 4605).

After destaging all dirty data accumulated in the disk cache of themigration source storage system 130 a to the external volume (step 4606;YES), the migration target storage system 130 b invalidates the mappingrelation between the device group in the storage system 130 b associatedwith the second expansion device and the virtual device in the storagesystem 130 b, and activates the mapping relation between the devicegroup in the storage system 130 b associated with the first expansiondevice and the virtual device in the storage system 130 b (step 4607).

The storage system 130 b permits access from the storage system 130 b tothe external volume on the one hand, and sets the inhibition of accessfrom the storage system 130 a to the external volume (access exclusivesetting) (step 4608).

The storage system 130 b activates the function for encrypting the datato be written in the external volume (step 4609).

The storage system 130 b deletes a path for connecting the secondexpansion device in the storage system 130 b and the migration sourcelogical unit in the storage system 130 a (step 4610).

When sharing the external volume with the migration source storagesystem 130 a and the migration target storage system 130 b (forinstance, when the migration source logical unit has a CVSconfiguration) (step 4611; YES), the migration source storage system 130a invalidates the mapping relation between the logical unit after themigration processing and the virtual device in the storage system 130 a(step 4612).

When the external volume is not to be shared with the migration sourcestorage system 130 a and the migration target storage system 130 b (step4611; NO), the storage system 130 a deletes the path for connecting thestorage system 130 a and the external volume (step 4613).

The migration source storage system 130 a deletes the expansion devicecreated in the storage system 130 a for virtualizing the externalvolume, the device group associated with such expansion device, thevirtual device associated with such device group, the logical deviceassociated with such virtual device, the logical unit associated withsuch logical device, and all paths connecting such logical unit and thehost computer 100 (step 4614).

The external storage system 150 inhibits access from the storage system130 a to the external volume (step 4615).

FIG. 47 shows the storage I/O processing routine. The storage I/Oprocessing routine is executed with the storage I/O processing program221.

The storage system 130 that received an I/O request from the hostcomputer 100 refers to the logical device management information 603,and confirms the access right of the host computer 100 (step 4701).

When the host computer 100 does not have an access right (step 4701;NO), the storage system 130 denies the I/O request (step 4708).

When the host computer 100 has an access right (step 4701; YES), thestorage system 130 refers to the logical device management information603 and determines whether a cache through mode is set (step 4702).

When the operation mode of the storage system 130 is a cache throughmode (step 4702; YES), and the I/O request from the host computer 100 isa write request (step 4703; YES), the storage system 130 writes the datareceived from the host computer 100 in the disk cache 134 (step 4704).

Thereafter, the storage system 130 writes data in the external volume(step 4705), updates the management information of cache data to destagecomplete (step 4706), and issues a write completion report to the hostcomputer 100 (step 4707).

When the operation mode of the storage system 130 is not a cache throughmode (step 4702; NO), the storage system 130 determines whether thelogical unit of the access destination is being migrated (step 4710).

When the logical unit of the access destination is not being migrated(step 4710; NO), the storage system 130 executes I/O processing to themigration source logical unit (step 4709), and issues a write completionreport to the host computer 100 (step 4707).

Meanwhile, when the logical unit of the access destination is beingmigrated (step 4710; YES), the storage system 130 determines whether themigration of the storage extent corresponding to the access address iscomplete (step 4711).

When the migration of the storage extent corresponding to the accessaddress is incomplete (step 4711; NO), the storage system 130 executesI/O processing to the migration source logical unit (step 4709), andissues a write completion report to the host computer 100 (step 4707).

When the migration of the storage extent corresponding to the accessaddress is complete (step 4711; YES), the storage system 130 executesI/O processing to the logical unit of the migration destination (step4712), and issues a write completion report to the host computer 100(step 4707).

FIG. 48 shows the host I/O processing routine. The host I/O processingroutine is executed with the host I/O processing program 261 in the hostcomputer 100.

The host computer 100 receives an I/O request to the device filecorresponding to the logical unit of the storage system 130 from theapplication program executed in the host computer 100 (step 4801).

The host computer 100 refers to the device path management information251, and determines whether a plurality of paths (multi path) are set inthe device file of the access destination (step 4802).

When a plurality of paths are not set (step 4802; NO), the host computer100 proceeds to the processing at step 4804 with the designated devicefile as the access target.

When a plurality of paths are set (step 4802; YES), the host computer100 decides the device file to be accessed based on the status of therespective paths and the priority of I/O sorting (step 4803).

Subsequently, the host computer 100 converts the device file to beaccessed and calculates the identifier and LUN of the storage system 130and the port 131 (step 4804).

The host computer 100 sends an I/O request to the storage system 130 ofthe access destination (step 4805).

When the I/O processing ends normally (step 4806; YES), the hostcomputer 100 issues an I/O processing completion report to theapplication program (step 4809).

When the I/O processing does not end normally (step 4806; NO), the hostcomputer 100 checks the existence of an alternate path (step 4807).

When there is an alternate path (step 4807; YES), the host computer 100reissues the I/O processing request to the storage system 130 by way ofthe alternate path (step 4808), and issues an I/O processing completionreport to the application program (step 4809).

When there is no alternate path (step 4807; NO), the host computer 100issues an I/O processing completion report to the application program(step 4809).

FIG. 49 shows the storage load monitoring processing routine. Thestorage load monitoring processing routine is executed for the purposeof checking the load of the respective storage systems 130, andmigrating a logical unit in the storage system 130 in a high load statusor performance deterioration status to another storage system 130. Thestorage load monitoring processing routine is executed with the storageload monitoring program 242 in the management server 110.

The management server 110 periodically acquires the configurationinformation of the storage system 130 by way of the IP network 175 (step4901), and checks whether there is a malfunction in the configuration ofthe respective storage systems 130 (step 4902).

When the I/O processing performance of a certain storage system 130deteriorates due to a failure in the disk cache 134 or the controlprocessor 132 (step 4902), the management server 110 decides the storagesystem 130 encountering performance deterioration as the migrationsource storage system 130 a (step 4908).

When a storage system 130 encountering performance deterioration cannotbe detected (step 4902; NO), the management server 110 periodicallyacquires operational information such as the I/O frequency from therespective storage systems 130 to the respective logical devices, andutilization ratio of the respective control processors 132 or the diskcache 134 (step 4903).

When the difference in the I/O load between the respective storagesystem 130 is above a prescribed level (step 4904; YES), the managementserver 110 decides the storage system 130 of a high load status as themigration source storage 130 a (step 4905).

The management server 110 selects a logical to become the migrationsource in relation to the migration source storage 130 a selected atstep 4905 or step 4908, selects the migration target storage 130 b andselects the logical unit to be migrated (step 4906), and commands thestorage systems 130 a, 130 b to migrate the logical unit (step 4907).

As a result of monitoring the load of the respective storage systems 130configuring the computer system 500 with the storage load monitoringprocessing routine, when a failure occurs in a certain storage system130 due to the malfunction of the disk cache 134 or the controlprocessor 132, or the I/O processing performance of the storage system130 deteriorates due to some reason, it is possible to maximize the I/Oprocessing performance of the overall computer system 500 by switchingthe control role of the external volume to a storage system 130 in anormal status or low load status.

Another method of the logical unit migration processing is now explainedwith reference to FIG. 50 to FIG. 54.

FIG. 50 shows the system configuration of a computer system 501. Thecomputer system 501 has a host computer 100, storage systems 130 a, 130b, and an external storage system 150. The systems which are the same asthose shown in FIG. 1 are given the same reference numeral, and thedetailed explanation thereof is omitted.

The operation mode of the storage system 130 a is set to a cache throughmode, and data to be stored in the external volume 301 is constantlykept up to date. The host computer 100 is able to migrate the logicalunit 201 a to the logical unit 201 b by merely switching the access pathfrom the path 401 to the path 403 without having to switch the mappingof the devices.

Incidentally, when the operation mode of the storage system 130 a is setto a write after mode, the I/O request from the host computer 100 to thestorage system 130 a is temporarily halted, and the dirty dataaccumulated in the disk cache of the storage system 130 a is destaged tothe external volume 301. Thereafter, the host computer 100 is able tomigrate the logical unit 201 a to the logical unit 201 b by merelyswitching the access path from the path 401 to the path 403 withouthaving to switch the mapping of the devices.

FIG. 51 shows the system configuration of a computer system 502. Thecomputer system 502 has a host computer 100, and storage systems 130 a,130 b. The storage system 130 a has a physical device 205 a associatedwith a storage resource having a real storage extent such as a diskdrive, and virtualizes the physical device 205 a as the logical unit 201a via the respective storage hierarchies (PDEV/VDEV/LDEV/LU). Meanwhile,the storage system 130 b has a physical device 205 b associated with astorage resource having a real storage extent such as a disk drive, andvirtualizes the physical device 205 b as the logical unit 201 b via therespective storage hierarchies (PDEV/VDEV/LDEV/LU). The logical unit 201b is scheduled to become the migration destination of the logical unit201 a.

In the computer system 502, a copy pair for performing synchronous copybetween the migration source logical unit 201 a and the migration targetlogical unit 201 b is set. By setting a copy pair like this, datawritten from the host computer 100 to the logical unit 201 a (actuallythe disk cache) is written in the logical unit 201 b (actually the diskcache) by way of a path (not shown) on the storage network, and a writecompletion report is thereafter issued to the host computer 100.

When a failure occurs in the storage system 130 a, the host computer 100is able to migrate the logical unit 201 a to the logical unit 201 bmerely by switching the access path from the path 401 to the path 403without having to switch the mapping of the devices.

FIG. 52 shows the system configuration of a computer system 503. Thecomputer system 503 has a host computer 100, and storage systems 130 a,130 b. The systems which are the same as those shown in FIG. 51 aregiven the same reference numeral, and the detailed explanation thereofis omitted.

The outline of processing for migrating data of the logical unit 201 a(migration source logical unit) in the storage system 130 a (migrationsource storage) to the logical unit 201 b (migration destination logicalunit) in the storage system 130 b (migration destination storage) is nowexplained. The logical unit migration processing includes the followingprocessing routine of (1) to (9).

(1) The storage system 130 b defines a path 404 for externallyconnecting the migration source logical unit 201 a and the migrationtarget storage system 130 b, and creates an expansion device 206 b forvirtualizing the logical unit 201 a in the storage system 130 b.(2) The storage system 130 b creates virtual devices 203 b-1, 203 b-2having a logical configuration that is the same as the logicalconfiguration of the virtual device 203 a in the storage system 130 b.(3) The storage system 130 b creates logical devices 202 b-1, 202 b-2having a logical configuration that is the same as the logicalconfiguration of the logical device 202 a in the storage system 130 b.(4) The storage system 130 b maps the expansion device 206 b to thevirtual device 203 b-1, and further maps the physical device 205 b tothe virtual device 203 b-2.(5) The storage system 130 b maps the virtual device 203 b-1 to thelogical device 202 b-1, and further maps the virtual device 203 b-2 tothe logical device 202 b-2.(6) The storage system 130 b creates a logical unit 201 b having alogical configuration that is the same as the logical configuration ofthe logical unit 201 a in the storage system 130 b, and defines a path403 for connecting the host computer 100 and the logical unit 201 b. Thelogical device 202 b-1 is mapped to the logical unit 201 b.(7) The host computer 100 switches the access path from the path 401 tothe path 403. Here, access from the host computer 100 to the logicalunit 201 a is inhibited such as by deleting the path 401. Incidentally,path switching from the path 401 to the path 403 may also be conductedby the storage systems 130 a, 130 b, or the management server 110.Further, it is not necessarily the case that the path 401 needs to bedeleted, and, for instance, the path 401 may be set as an alternate path(for instance, a path to be used during system failure) of the path 403,and the path 401 may be left as is with the path 401 in an invalidstate.(8) The storage system 130 b copies the logical device 202 b-1 to thelogical device 202 b-2. As a result of the foregoing processing, it ispossible to synchronize the physical device 205 a and the physicaldevice 205 b.

Incidentally, the data I/O path from the host computer 100 to thestorage system 130 b during the logical unit migration processing willbe path 403→storage hierarchy (LU/LDEV/VDEV/EDEV) in the storage system130 b →path 404→storage hierarchy (LU/LDEV/VDEV/PDEV) in the storagesystem 130 a.

(9) If the storage system 130 b is able to synchronize the physicaldevice 205 a and the physical device 205 b, it releases the mappingrelation between the virtual device 203 b-2 and the logical device 202b-2, and maps the virtual device 203 b-2 to the logical device 202 b-1.Further, the storage system 130 b releases the mapping relation betweenthe virtual device 203 b-1 and the logical device 202 b-1, and maps thevirtual device 203 b-1 to the logical device 202 b-2. Further, thestorage system 130 b deletes the path 404.

FIG. 53 shows the system configuration of a computer system 504. Thecomputer system 504 has a host computer 100, storage systems 130 a, 130b, and an external storage system 150. The systems which are the same asthose shown in FIG. 52 are given the same reference numeral, and thedetailed explanation thereof is omitted.

The primary difference between the computer system 504 and the foregoingcomputer system 503 is as follows. In other words, the storage system130 a has an expansion device 206 a in substitute for the physicaldevice 205 a. The expansion device 206 a is a virtual storage extent forvirtualizing the external volume 301. The logical unit migrationprocessing routine to be executed by the computer system 504 is the sameas the logical unit migration processing routine to be executed by thecomputer system 503.

FIG. 54 shows the system configuration of a computer system 505. Thecomputer system 505 has a host computer 100, storage systems 130 a, 130b, and an external storage system 150. The systems which are the same asthose shown in FIG. 52 are given the same reference numeral, and thedetailed explanation thereof is omitted.

The primary difference between the computer system 505 and the foregoingcomputer system 503 is as follows. In other words, the storage system130 a has an expansion device 206 c in substitute for the physicaldevice 205 a. The expansion device 206 c is a virtual storage extent forvirtualizing the external volume 301. The logical unit migrationprocessing routine to be executed by the computer system 505 is the sameas the logical unit migration processing routine to be executed by thecomputer system 503.

The computer systems 506, 507 having a function of migrating a part ofthe logical unit from the migration source storage to the migrationdestination storage is now explained with reference to FIG. 55 and FIG.56.

FIG. 55 shows the system configuration of a computer system 506. Thecomputer system 506 has a host computer 100, storage systems 130 a, 130b, and an external storage system 150. The systems which are the same asthose shown in FIG. 1 are given the same reference numeral, and thedetailed explanation thereof is omitted.

The external volume 301 is partitioned into a plurality of storageextents 301-1, 301-2. The respective storage extents 301-1, 301-2 arepartitions for partitioning the external volume 301. An independent filesystem can be created in the respective storage extents 301-1, 301-2.For example, the storage extent 301-1 corresponds to the C drive, andthe storage extent 301-2 corresponds to the D drive.

The logical unit 201 a provided by the storage system 130 a to the hostcomputer 100 via the path 401 is a virtualization of the external volume301, and is partitioned into a plurality of storage extents 201 a-1, 201a-2. The storage extent 201 a-1 is a virtualization of the storageextent 301-1. The storage extent 201 a-2 is a virtualization of thestorage extent 301-2.

Further, in order to migrate a part (for example, storage extent 201 a-2corresponding to the D drive) of the logical unit 201 a from the storagesystem 130 a to the storage system 130 b, the logical unit 201 a ismigrated from the storage system 130 a to the storage system 130 b basedon a routine that is the same as the foregoing processing routine of (1)to (9). The logical information of the logical unit 201 b created in thestorage system 130 b is the same as the logical configuration of thelogical unit 201 a. In other words, the logical unit 201 b provided bythe storage system 130 b to the host computer 100 via the path 403 is avirtualization of the external volume 301, and is partitioned into aplurality of storage extents 201 b-1, 201 b-2. The storage extent 201b-1 is a virtualization of the storage extent 301-1. The storage extent201 b-2 is a virtualization of the storage extent 301-2.

Here, by setting the system configuration of the computer system 506 toinhibit access from the host computer 100 to the storage extent 201 a-2and inhibit access from the host computer 100 to the storage extent 201b-1, it will be possible to migrate a part of the logical unit 201 afrom the storage system 130 a to the storage system 130 b.

Incidentally, it is necessary to inhibit access from the storage system130 a to the storage extent 301-2, and inhibit access from the storagesystem 130 b to the storage extent 301-1.

The link manager 108 in the host computer 100 switches the pathaccording to the access destination. For instance, the link manager 108selects the path 401 when the host computer 100 is to access the Cdrive, and selects the path 403 when the host computer 100 is to accessthe D drive.

FIG. 56 shows the system configuration of a computer system 507. Thecomputer system 507 has a host computer 100, storage systems 130 a, 130b, and an external storage system 150. The systems which are the same asthose shown in FIG. 55 are given the same reference numeral, and thedetailed explanation thereof is omitted.

The basic system configuration of the computer system 507 is roughly thesame as the system configuration of the computer system 506, anddifferences of the two will be mainly explained. The external volume 301is partitioned into a plurality of storage extents 301-1, 301-2, 301-3.The storage extent 301-3 is a shared extent virtualized with therespective logical units 201 a, 201 b. The storage extent 201 a-3 of thelogical unit 201 a is a virtualization of the storage extent 301-3 ofthe external volume 301. Further, the storage extent 201 b-3 of thelogical unit 201 b is a virtualization of the storage extent 301-3 ofthe external volume 301.

The host computer 100 has two paths as the access path to the storageextent 301-3 as a shared extent of the external volume 301; namely, apath for access via the logical unit 201 a, and a path for access viathe logical unit 201 b. The storage extent 301-3, for instance, storesimportant data upon the host computer 100 performing businessactivities. Since the host computer 100 has a plurality of paths foraccessing the storage extent 301-3, even if a failure occurs to one ofthe paths, it will still be able to access the storage extent 301-3 byway of the other path.

Three systems for virtualizing the storage extent 301-3 as a sharedextent of the external volume 301 with a plurality of logical units 201a, 201 b are now explained.

(1) First System

The operation mode of the respective storage systems 130 a, 130 b is setto a cache through mode. When the host computer 100 writes data in thestorage extent 301-3 as a shared extent of the external volume 301 viathe logical unit 201 a or the logical unit 201 b, a write completionreport is issued to the host computer 100 after the data in the storageextent 301-3 is updated. Since data to be stored in the storage extent301-3 is constantly kept up to date, even if the host computer 100accesses the shared extent of the external volume 301 via the logicalunit 201 a, or even if the host computer 100 accesses the shared extentof the external volume 301 via the logical unit 201 b, there will be noinconsistent data in the shared extent.

(2) Second System

A copy pair for bidirectionally performing synchronous copy between thestorage extent 201 a-3 of the logical unit 201 a and the storage extent201 b-3 of the logical unit 201 b is set. As a result of this setting,when the host computer 100 updates the data in the storage extent 201a-3 of the logical unit 201 a in order to update the data of the storageextent 301-3 as the shared extent of the external volume 301, the datain the storage extent 201 b-3 of the logical unit 201 b is similarlyupdated. Further, when the host computer 100 updates the data in thestorage extent 201 b-3 of the logical unit 201 b, data in the storageextent 201 a-3 of the logical unit 201 a is similarly updated.

(3) Third System

The storage extent 206 a-3 corresponding to the shared extent among thestorage extents of the expansion device 206 a for virtualizing theexternal volume 301 is associated with the storage extent 201 a-3 of thelogical unit 201 a, and is also associated with the storage extent 201b-3 of the logical unit 201 b. Similarly, the storage extent 206 b-3corresponding to the shared extent among the storage extents of theexpansion device 206 b for virtualizing the external volume 301 isassociated with the storage extent 201 b-3 of the logical unit 201 b,and is also associated with the storage extent 201 a-3 of the logicalunit 201 a. Like this, by bidirectionally applying the externalconnecting technology, when the host computer 100 updates the data inthe storage extent 201 a-3 of the logical unit 201 a, the data in thestorage extent 201 b-3 of the logical unit 201 b is similarly updated.Further, when the host computer 100 updates the data in the storageextent 201 b-3 of the logical unit 201 b, the data in the storage extent201 a-3 of the logical unit 201 a is similarly updated.

Incidentally, in the third system, it is necessary to differentiate thehost access and the access via external connection in order to avoidendless loop processing.

Like this, when the external volume 301 is virtualized with a pluralityof logical units, a configuration may be adopted where a certain storageextent configuring the external volume 301 is accessible via a certainlogical unit, and another storage extent (shared extent) is accessiblevia a plurality of logical units. Synchronous copy or asynchronous copymay be applied to a storage extent corresponding to a shared extentamong the respective storage extents of a plurality of logical units.

The computer systems 508, 509 that have a slightly different systemconfiguration of the computer system 500 from the perspective of highavailability are now explained with reference to FIG. 57 and FIG. 58.

FIG. 57 shows the system configuration of a computer system 508. Thecomputer system 508 has a host computer 100, storage systems 130 a, 130b, and an external storage system 150. The host computer 100, thestorage systems 130 a, 130 b, and the external storage system 150 aremutually connected via a storage network (not shown) such as an FC-SAN.The storage system 130 a functions as a preferred system (operationalsystem), and the storage system 130 b functions as an alternate system(standby system). The storage systems 130 a, 130 b share the externalvolume 301 in the external storage system 150.

The storage system 130 a has a plurality of storage hierarchies (logicalunit 201 a, logical device 202 a, virtual device 203 a, and expansiondevice 206 a) for virtualizing the external volume 301. The expansiondevice 206 a is a virtualization of the external volume 301, and isconnected to the external storage system 150 via the path 402. Theexpansion device 206 a is mapped to the virtual device 203 a. Thevirtual device 203 a is mapped to the logical device 202 a. The logicaldevice 202 a is mapped to the logical unit 201 a. The logical unit 201 ais connected to the host computer 100 via the path 401. The operationmode of the storage system 130 a is set to a cache through mode, and theexternal volume 301 constantly stores latest data accompanying the hostaccess.

Meanwhile, the storage system 130 b has a plurality of storagehierarchies (logical unit 201 b, logical device 202 b, virtual device203 b, and expansion device 206 b) for virtualizing the external volume301. The expansion device 206 b is a virtualization of the externalvolume 301, and is connected to the external storage system 150 via thepath 405. The expansion device 206 b is mapped to the virtual device 203b. The virtual device 203 b is mapped to the logical device 202 b. Thelogical device 202 b mapped to the logical unit 201 b. The logical unit201 b is connected to the host computer 100 via the path 403. The path403 is in an alternate path relation with the path 401. The operationmode of the storage system 130 b may be a cache through mode, or a writeafter mode.

Incidentally, in the foregoing system configuration, when a failureoccurs in the preferred storage system 130 a, the host computer 100switches the path 401 to the path 403, and issues an I/O request to thealternate storage system 130 b. Since the operation mode of the storagesystem 130 a is set to a cache through mode as described above, the diskcache in the storage system 130 a does not contain data that has notbeen destaged to the external volume 301. Thus, when the host computer100 detects that a failure has occurred in the preferred storage system130 a, is it able to immediately switch the destination of issuing theI/O request to the alternate storage system 130 b.

FIG. 58 shows the system configuration of a computer system 509. Thecomputer system 509 has a host computer 100, storage systems 130 a, 130b, and an external storage system 150. The systems which are the same asthose shown in FIG. 57 are given the same reference numeral, and thedetailed explanation thereof is omitted.

The storage system 130 a has a plurality of storage hierarchies (logicalunit 201 a, logical device 202 a, virtual device 203 a, and expansiondevices 206 a, 206 d) for virtualizing the external volume 301. Theexpansion device 206 a is a virtualization of the external volume 301,and is connected to the external storage system 150 via the path 402.The expansion device 206 a is a virtualization of the logical unit 201b, and is connected to the storage system 130 b via the path 410. Theexpansion devices 206 a, 206 d are mapped to the virtual device 203 a.The virtual device 203 a is mapped to the logical device 202 a. Thelogical device 202 a is mapped to the logical unit 201 a. The logicalunit 201 a is connected to the host computer 100 via the path 401.

Meanwhile, the storage system 130 b has a plurality of storagehierarchies (logical unit 201 b, logical device 202 b, virtual device203 b, and expansion device 206 b) for virtualizing the external volume301. The expansion device 206 b is a virtualization of the externalvolume 301, and is connected to the external storage system 150 via thepath 405. The expansion device 206 b is mapped to the virtual device 203b. The virtual device 203 b is mapped to the logical device 202 b. Thelogical device 202 b mapped to the logical unit 201 b. The logical unit201 b is connected to the host computer 100 via the path 403. The path403 is in an alternate path relation with the path 401.

The three systems for increasing the availability of the computer system509 are now explained.

(1) First System

The respective operation modes of the preferred storage system 130 a andthe alternate storage system 130 b are set to a cache through mode.Then, the data I/O path from the host computer 100 to the logical unit201 a will be path 401→storage hierarchy (LU/LDEV/VDEV/EDEV) in thestorage system 130 a →path 410→storage hierarchy (LU/LDEV/VDEV/EDEV) inthe storage system 130 b →path 405→external volume 301. Nevertheless, asa path for performing read access from the host computer 100 to thelogical unit 201 a, for instance, a path that will be path 401→storagehierarchy (LU/LDEV/VDEV/EDEV) in the storage system 130 a →path402→external volume 301 may be employed.

According to the first system, since the external volume 301 willconstantly store latest data accompanying the host access, even if afailure occurs in the preferred storage system 130 a, the host computer100 will be able to immediately use the alternate storage system 130 bby immediately switching from the path 401 to the path 403.

(2) Second System

The data I/O operation between the logical unit 201 a in the preferredstorage system 130 a and the logical unit 201 b in the alternate storagesystem 130 b is set to a cache through mode. In other words, datawritten from the host computer 100 to the logical unit 201 a (actuallythe disk cache) is written in the logical unit 201 b (actually the diskcache) by way of the path 401 from the storage hierarchy(LU/LDEV/VDEV/EDEV) in the storage system 130 a, and a write completionreport is thereafter issued to the host computer 100. Meanwhile, thedata I/O operation between the logical unit 201 a in the preferredstorage system 130 a and the external volume 301 is set to a write aftermode. In other words, data written from the host computer 100 to thelogical unit 201 a (actually the disk cache) is destaged to the externalvolume 301 after a write completion report is issued to the hostcomputer 100.

While the preferred storage system 130 a is operating normally, only thestorage system 130 a will have an access right to the external volume301, and the alternate storage system 130 b will not have an accessright to the external volume 301. When the storage system 130 b receivesfrom the storage system 130 a a notice to the effect that the storagesystem 130 a wrote data in the external volume 301, the storage system130 b deletes the data written from the storage system 130 a in thelogical unit 201 b (actually the disk cache).

According to the second system, in addition to the preferred storagesystem 130 a, the alternate storage system 130 b is also able to retainthe dirty data that is not destaged to the external volume 301. Thus,when a failure occurs in the preferred storage system 130 a, thealternate storage system 130 b is able to keep the data stored in theexternal volume 301 up to date by acquiring an access right to theexternal volume 301 and destaging the dirty data to the external volume301. After updating the data stored in the external volume 301 to thelatest state, the host computer 100 is able to issue an I/O request tothe alternate storage system 130 b by switching from the path 401 to thepath 403.

(3) Third System

A copy pair for performing synchronous copy is formed between thelogical unit 201 a in the preferred storage system 130 a and the logicalunit 201 b in the alternate storage system 130 b. As a result of settinga copy pair as described above, data written from the host computer 100to the logical unit 201 a (actually the disk cache) is written in thelogical unit 201 b (actually the disk cache) by way of a path (notshown) on the storage network, and a write completion report isthereafter issued to the host computer 100. Meanwhile, the data I/Ooperation between the logical unit 201 a in the preferred storage system130 a and the external volume 301 is set to a write after mode. In otherwords, data written from the host computer 100 to the logical unit 201 a(actually the disk cache) is destaged to the external volume 301 after awrite completion report is issued to the host computer 100.

While the preferred storage system 130 a is operating normally, only thestorage system 130 a will have an access right to the external volume301, and the alternate storage system 130 b will not have an accessright to the external volume 301. When the storage system 130 b receivesfrom the storage system 130 a a notice to the effect that the storagesystem 130 a wrote data in the external volume 301, the storage system130 b deletes the data written from the storage system 130 a in thelogical unit 201 b (actually the disk cache). This is the same as in thesecond system.

According to the third system, in addition to the preferred storagesystem 130 a, the alternate storage system 130 b is also able to retainthe dirty data that is not destaged to the external volume 301. Thus,when a failure occurs in the preferred storage system 130 a, thealternate storage system 130 b is able to keep the data stored in theexternal volume 301 up to date by acquiring an access right to theexternal volume 301 and destaging the dirty data to the external volume301. After updating the data stored in the external volume 301 to thelatest state, the host computer 100 is able to issue an I/O request tothe alternate storage system 130 b by switching from the path 401 to thepath 403.

FIG. 59 shows the system configuration of a computer system 580 as amodified example of the present embodiment. The computer system 580 hasa system configuration of replacing the storage systems 130 a, 130 bwith the virtualization devices 180 a, 180 b, 180 c in the systemconfiguration of the computer system 500 (refer to FIG. 2). For theconvenience of explanation, the virtualization devices 180 a, 180 b, 180c are collectively referred to as a virtualization device 180. Thevirtualization device 180 has a port 181 for connection to the fibrechannel switch 120 via the storage network, a controller processor 182for controlling the processing of virtualizing the external volume 301,a memory 182 for storing control programs and the like of executing thecontrol processor 182, and a port 184 for connecting to the managementserver 110 via the IP network 175. The virtualization device 180, forexample, is an exclusive virtualization device or a virtualization witha function for virtualizing the switch storage resource. Thevirtualization device 180 has a function for providing to the hostcomputer 100 a logical unit configured by virtualizing the externalvolume 301.

The computer system 580, for example, is able to migrate a logical unit,which is provided by the virtualization device 180 a to the hostcomputer 100, to the virtualization device 180 b. Outline of the logicalunit migration processing from the virtualization device 180 a to thevirtualization device 180 b is roughly the same as the processingcontents described above. Nevertheless, since the virtualization device180 does not have a disk cache for temporarily storing data written inthe external volume 301, not only is it not necessary to set theoperation mode of the virtualization device 180 to a cache through mode,it is not necessary to wait for the destaging from the virtualizationdevice 180 to the external volume 301 to be complete. It is possible tocomplete the migration processing merely by succeeding the attributesset in the logical unit provided by the migration source virtualizationdevice 180 a to the host computer 100 in the logical unit provided bythe migration target virtualization device 180 b to the host computer100.

1. A computer system, comprising: a host computer; an external storagesystem having an external volume storing data used by said hostcomputer; a first storage system having a first expansion deviceconfigured by virtualizing said external volume via a first path betweensaid external device and said first storage system, providing a firstlogical unit corresponding to said first expansion device to said hostcomputer, and controlling access to said first logical unit from saidhost computer; and a second storage system having a second expansiondevice configured by virtualizing said external volume via a second pathbetween said external device and said second storage system, providing asecond logical unit corresponding to said second expansion device tosaid host computer, and controlling access to said second logical unitfrom said host computer, wherein said first storage system furtherincludes: a third expansion device configured by virtualizing saidsecond logical unit of said second storage system via a third pathbetween said first and said second storage systems, and wherein if saidfirst storage system receives write data to said first logical unit,said first storage system stores data in said external volume byaccessing said external volume via said third expansion device, saidthird path, said second expansion device, and said second path, by usingcache through mode.
 2. The computer system according to claim 1, whereinsaid host computer switches access to data stored in said externalvolume by using said second logical unit instead of said first logicalunit, when a failure occurs in said first storage system.
 3. Thecomputer system according to claim 1, wherein if said first storagesystem receives read access to said first logical unit, said firststorage system controls to read data from said external volume byaccessing via said first expansion device and said first path.
 4. Acomputer system, comprising: a host computer; an external storage systemhaving an external volume storing data used by said host computer; afirst storage system having a first expansion device configured byvirtualizing said external volume via a first path between said externaldevice and said first storage system, providing a first logical unitcorresponding to said first expansion device to said host computer, andcontrolling access to said first logical unit from said host computer;and a second storage system having a second expansion device configuredby virtualizing said external volume via a second path between saidexternal device and said second storage system, providing a secondlogical unit corresponding to said second expansion device to said hostcomputer, and controlling access to said second logical unit from saidhost computer, wherein said first storage system further includes: athird expansion device configured by virtualizing said second logicalunit of said second storage system via a third path between said firstand said second storage system, wherein said first storage system onlyhas an access authority to said external volume, wherein if said firststorage system receives write data to said first logical unit, saidfirst storage system stores data in said second logical unit byaccessing via said third expansion device and said third path, by usingcache through mode, and wherein said second storage system deletes datastored in said second logical unit after said first storage systemdestages dirty data from said first logical unit to said externalvolume.
 5. The computer system according to claim 4, wherein said hostcomputer switches access to data stored in said external volume by usingsaid second logical unit instead of said first logical unit, when afailure occurs in said first storage system.
 6. The computer systemaccording to claim 5, wherein said second storage system retrieves anaccess authority to said external volume, destages dirty data stored insaid second logical unit to said external volume.
 7. The computer systemaccording to claim 4, wherein said second logical unit relates to saidfirst logical volume as a copy pair for performing synchronous copy.